METHYLENE CHLORIDE
r
c
Agency for Toxic Substances and Disease Registry
U.S. Public Health Service
-------
ATSDR/TP-88/18
TOXICOLOGICAL PROFILE FOR
METHYLENE CHLORIDE
Date Published — April 1989
Prepared by:
Life Systems, Inc.
under Contract No. 68-02-4228
for
Agency for Toxic Substances and Disease Registry (ATSDR)
U.S. Public Health Service
in collaboration with
U.S. Environmental Protection Agency (EPA)
Technical editing/document preparation by:
Oak Ridge National Laboratory
under
DOE Interagency Agreement No. I857-B026-AI
-------
DISCLAIMER
Mention of company name or product does not constitute endorsement by
the Agency for Toxic Substances and Disease Registry.
-------
FOREWORD
The Superfund Amendments and Reauthorizacion Act of 1986 (Public
Law 99-499) extended and amended the Comprehensive Environmental
Response, Compensation, and Liability Act of 1980 (CERCLA or Superfund)
This public law (also known as SARA) directed the Agency for Toxic
Substances and Disease Registry (ATSDR) to prepare toxicological
profiles for hazardous substances which are most commonly found at
facilities on the CERCLA National Priorities List and which pose the
most significant potential threat to human health, as determined by
ATSDR and the Environmental Protection Agency (EPA). The list of the 100
most significant hazardous substances was published in the Federal
RegLscer on April 17, 1987.
Section 110 (3) of SARA directs the Administrator of ATSDR to
prepare a toxicological profile for each substance on the list. Each
profile must include the following content:
"(A) An examination, summary, and interpretation of available
toxicological information and epidemiologic evaluations on a
hazardous substance in order to ascertain the levels of significant
human exposure for the substance and the associated acute,
subacute, and chronic health effects.
(B) A determination of whether adequate information on the health
effects of each substance is available or in the process of
development to determine levels of exposure which present a
significant risk to human health of acute, subacute, and chronic
health effects.
(C) Where appropriate, an identification of toxicological testing
needed to identify the types or levels of exposure that may present
significant risk of adverse health effects in humans."
This toxicological profile is prepared in accordance with
guidelines developed by ATSDR and EPA. The guidelines were published in
the Federal Register on April 17, 1987. Each profile will be revised and
republished as necessary, but no less often than every three years, as
required by SARA.
The ATSDR toxicological profile is intended to characterize
succinctly the toxicological and health effects information for the
hazardous substance being described. Each profile identifies and reviews
the key literature that describes a hazardous substance's toxicological
properties. Other literature is presented but described in less detail
than the key studies. The profile is not intended to be an exhaustive
document; however, more comprehensive sources of specialty information
are referenced.
ILL
-------
Foreword
Each toxlcological profile begins with a public health statement,
which describes in nontechnical language a substance's relevant
toxicological properties. Following the statement is material that
presents levels of significant human exposure and, where known,
significant health effects. The adequacy of information to determine a
substance's health effects is described in a health effects summary.
Research gaps in toxicologic and health effects information are
described in the profile. Research gaps that are of significance to
protection of public health will be identified by ATSDR, the National
Toxicology Program of the Public Health Service, and EPA. The focus of
the profiles is on health and toxicological information; therefore, we
have included this information in the front of the document.
The principal audiences for the toxicological profiles are health
professionals at the federal, state, and local levels, interested
private sector organizations and groups, and members of the public. We
plan to revise these documents in response to public comments and as
additional data become available; therefore, we encourage comment that
will make the toxicological profile series of the greatest use.
This profile reflects our assessment of all relevant toxicological
testing and information that has been peer reviewed. It has been
reviewed by scientists from ATSDR, EPA, the Centers for Disease Control,
and the National Toxicology Program. It has also been reviewed by a
panel of nongovernment peer reviewers and was made available for public
review. Final responsibility for the contents and views expressed in
this toxicological profile resides with ATSDR.
James 0. Mason, M.D., Dr. P.H.
Assistant Surgeon General
Administrator, ATSDR
iv
-------
CONTENTS
FOREWORD iii
LIST OF FIGURES '. . . ix
LIST OF TABLES xi
1. PUBLIC HEALTH STATEMENT 1
1.1 WHAT IS METHYLENE CHLORIDE? 1
1.2 HOW MIGHT I BE EXPOSED TO METHYLENE CHLORIDE? 1
1.3 HOW DOES METHYLENE CHLORIDE GET INTO MY BODY? 1
1.4 HOW CAN METHYLENE CHLORIDE AFFECT MY HEALTH? 1
1.5 IS THERE A MEDICAL TEST TO DETERMINE IF I HAVE BEEN
EXPOSED TO METHYLENE CHLORIDE? 2
1.6 WHAT LEVELS OF EXPOSURE HAVE RESULTED IN HARMFUL
HEALTH EFFECTS , 2
1.7 WHAT RECOMMENDATIONS HAS THE FEDERAL GOVERNMENT
MADE TO PROTECT HUMAN HEALTH? 5
2. HEALTH EFFECTS SUMMARY 7
2.1 INTRODUCTION 7
2.2 LEVELS OF SIGNIFICANT HUMAN EXPOSURE 8
2.2.1 Key Studies 8
2.2.1.1 Lethality 16
2.2.1.2 Systemic/target organ toxicity 16
2.2.1.3 Developmental toxicity 18
2.2.1.4 Genotoxicity 18
2.2.1.5 Reproductive toxicity 18
2.2.1.6 Carcinogenicity 19
2.2.1.7 Mechanisms of action 20
2.2.2 Biological Monitoring as a Measure of Exposure
and Effects 21
2.2.3 Environmental Levels as Indicators of Exposure
and Effects 21
2.2.3.1 Levels found in the environment 21
2.2.3.2 Human exposure potential 22
2.3 ADEQUACY OF DATABASE 22
2.3.1 Introduction 22
2.3.2 Health Effect End Points 23
2.3.2.1 Introduction and graphic summary 23
2.3.2.2 Description of highlights of graphs 23
2.3.2.3 Summary of relevant ongoing research .... 23
2.3.3 Other Information Needed for Human
Health Assessment 26
2.3.3.1 Pharmacokinetics and mechanisms of
action 26
2.3.3.2 Monitoring of human biological samples .. 26
2.3.3.3 Environmental considerations 26
-------
Concents
3. PHYSICAL AND CHEMICAL INFORMATION 27
3 .1 CHEMICAL IDENTITY ' ' 27
3 . 2 PHYSICAL AND CHEMICAL PROPERTIES '.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'. 27
4. TOXICOLOGICAL DATA 31
4.1 OVERVIEW 31
4. 2 TOXICOKINETICS '.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'. 32
4.2.1 Overview 32
4.2.2 Absorption 33
4.2.2.1 Inhalation '.'.'.'.'.'. 33
4.2.2.2 Oral 34
4.2.2.3 Dermal 35
4.2.3 Distribution " 35
4.2.3.1 Inhalation 35
4.2.3.2 Oral '.'.'.'.'.'.'.'.'. 36
4.2.3.3 Dermal 35
4.2.4 Metabolism '.'.'.'.'.'.'.'.'.'.'.'. 36
4.2.4.1 Inhalation 36
4.2.4.2 Oral '.'.'.'.'.'.'.'.'. 42
4.2.4.3 Dermal 43
4.2.4.4 In vitro studies 44
4.2.5 Excretion 44
4.2.5.1 Inhalation 44
4.2.5.2 Oral '.'.'.'.'.'.'.'.'.'. 46
4.2.5.3 Dermal 46
4.2.6 Discussion 45
4. 3 TOXICITY '.'.'.'.'.'.'.'.'.'.'.'.'. 47
4.3.1 Overview 47
4.3.2 Lethality and Decreased Longevity 47
4.3.2.1 Overview 47
4.3.2.2 Inhalation 47
4.3.2.3 Oral "'"' 43
4.3.2.4 Dermal 48
4.3.2.5 Discussion 48
4.3.3 Systemic/Target Organ Toxicity 48
4.3.3.1 Overview 43
4.3.3.2 Central nervous system 50
4.3.3.3 Hepatotoxicity 53
4.3.3.4 Renal effects 58
4.3.3.5 Respiratory effects 59
4.3.3.6 Cardiovascular 59
4.3.3.7 Ocular effects 60
4.3.4 Developmental Toxicity 60
4.3.4.1 Overview 60
4.3.4.2 Inhalation 60
4.3.4.3 Oral 61
4.3.4.4 Dermal 61
4.3.4.5 Discussion 61
4.3.5 Reproductive Toxicity 61
4.3.5.1 Inhalation 61
4.3.5.2 Oral 62
4.3.5.3 Dermal 62
4.3.5.4 Discussion 62
4.3.6 Genotoxicity 62
vi
-------
Concents
4.3.7 Carcinogenicity 65
4.3.7.1 Overview 65
4.3.7.2 Human 65
4.3.7.3 Animal 66
4.4 INTERACTIONS WITH OTHER CHEMICALS 68
5. MANUFACTURE, IMPORT, USE, AND DISPOSAL 69
5.1 OVERVIEW 69
5.2 PRODUCTION 69
5.3 IMPORT 69
5.4 USE 69
5.5 DISPOSAL 70
6. ENVIRONMENTAL FATE 71
6 .1 OVERVIEW " 71
6 . 2 RELEASES TO THE ENVIRONMENT 71
6.2.1 Anthropogenic Sources 71
6.2.2 Natural Sources 72
6.3 ENVIRONMENTAL FATE 72
6.3.1 Atmospheric Fate Processes 72
6.3.2 Surface Water/Groundwater Fate Processes 72
6.3.3 Soil Fate Processes 73
6.3.4 Biotic Fate Processes 73
7. POTENTIAL FOR HUMAN EXPOSURE 75
7.1 OVERVIEW 75
7.2 LEVELS MONITORED OR ESTIMATED IN THE ENVIRONMENT 75
7.2.1 Levels in Air 75
7.2.2 Levels in Water 76
7.2.3 Levels in Soil 76
7.2.4 Levels in Food 76
7.2.5 Resulting Exposure Levels 76
7.3 OCCUPATIONAL EXPOSURES 77
7.4 CONSUMER EXPOSURE 77
7. 5 POPULATIONS AT HIGH RISK 80
7.5.1 Above-Average Exposure 80
7.5.2 Above-Average Sensitivity 80
8. ANALYTICAL METHODS 81
8.1 ENVIRONMENTAL MEDIA 81
8.1.1 Air 81
8.1.2 Water 83
8.1.3 Soil 83
8.1.4 Food 83
8.2 BIOMEDICAL SAMPLES 83
8.2.1 Fluids and Exudates 83
8.2.2 Tissues 83
9. REGULATORY AND ADVISORY STATUS 85
9.1 INTERNATIONAL 85
9.2 NATIONAL 85
9.2.1 Regulations 85
9.2.2 Advisory Guidance 88
9.2.3 Data Analysis 89
9.2.3.1 References doses 89
9.2.3.2 Carcinogenic potency 90
vll
-------
Concents
9.3 STATE 9Q
9.3.1 Regulations 90
9.3.2 Advisory Guidance 90
10. REFERENCES 91
11. GLOSSARY 107
APPENDIX: PEER REVIEW m
viii
-------
LIST OF FIGURES
1.1 Health effects from breathing methylene chloride 3
1.2 Health effects from ingesting methylene chloride 4
2.1 Effects of methylene chloride--inhalation exposure 12
2.2 Levels of significant exposure for methylene chloride--
inhalation 13
2.3 Effects of methylene chloride--oral exposure 14
2.4 Levels of significant exposure for methylene chloride--
oral 15
2.5 Availability of information on health effects of methylene
chloride (human data) 24
2.6 Availability of information on health effects of methylene
chloride (animal data) 25
4.1 Proposed pathways for methylene chloride metabolism 45
-------
LIST OF TABLES
2 1 Key dose response data for short- terra CNS effects
of methylene chloride ................................... 1-0
2.2 Key dose response data for long-term hepatotoxicity
effects of methylene chloride ............................... 11
3 1 Chemical identity of methylene chloride .................... 28
3 2 Physical and chemical properties of methylene chloride ...... 29
4.1 Comparison of average daily values of dose surrogates
in lung and liver tissue of female B6C3F1 mice in
two chronic bioassays ....................................... 41
4 . 2 Acute lethality of methylene chloride ....................... 49
4.3 Short- terra experimental methylene chloride inhalation
exposures and reported effects in humans ..................... 51
4.4 Longer-term occupational methylene chloride inhalation
exposures and effects in humans .............................. 52
4.5 Short-term methylene chloride inhalation exposures
and effects in animals ...................................... 54
4.6 Longer-term methylene chloride inhalation exposures
and effects in animals ....................................... 57
4.7 Results of methylene chloride testing in various
mammalian short-term tests .................................. 63
4.8 Summary of primary tumors in rats and mice in
2 -year studies of methylene chloride ......................... 67
7.1 Occupations in which methylene chloride exposures
may occur [[[ 78
7.2 Summary of occupational exposure to methylene chloride ....... 79
8.1 Analytical methods for methylene chloride in environmental
samples [[[ 82
8.2 Analytical methods for methylene chloride in biological
-------
1. PUBLIC HEALTH STATEMENT
1.1 WHAT IS METHYLENE CHLORIDE?
Methylene chloride, also known as dichloromethane (DCM), is an
organic solvent that looks like water, has a mild sweet odor, and
evaporates very quickly. It is widely used as an industrial solvent and
as a paint stripper. It is also a component in certain aerosol and
pesticide products and is used in the manufacture of photographic film.
1.2 HOW MIGHT I BE EXPOSED TO METHYLENE CHLORIDE?
The highest exposures to DCM usually occur in workplaces where DCM
is used or from contact with consumer products that contain DCM;
exposure to this solvent in outdoor air and water is generally low.
Hobby and household use of paint-stripping chemicals and DCM-containing
aerosol products are major sources of exposure. Exposure occurs as a
result of breathing the vapors given off by the product or from direct
contact of the product material with the skin. Special efforts should be
taken to follow label directions that recommend working in a well-
ventilated area when using products containing DCM. Also, some
decaffeinated coffee and spices contain small amounts of DCM; however,
exposures from these sources are considered insignificant.
1.3 HOW DOES METHYLENE CHLORIDE GET INTO MY BODY?
Methylene chloride may enter the body when it is inhaled or
ingested. No data are currently available on the absorption of DCM
through human skin. Since DCM vaporizes very quickly, the primary route
of exposure is through inhalation. Once DCM enters the body, it is
absorbed through body membranes (e.g., stomach, intestines, and lungs)
and quickly enters the bloodstream.
1.4 HOW CAN METHYLENE CHLORIDE AFFECT MY HEALTH?
High levels of DCM in air (above about 500 ppm) can irritate the
eyes, nose, and throat. If DCM gets on the skin, it usually evaporates
quickly and causes only mild irritation. However, DCM can be trapped
against the skin by gloves, shoes, or clothes and can cause a burn. If
DCM gets into the eyes, it may cause a severe (but temporary) eye
irritation.
Methylene chloride can affect the central nervous system (brain).
If DCM is breathed at levels above about 500 ppm (500 parts DCM per 1
million parts air), it may cause effects much like those produced by
alcohol, including sluggishness, irritability, lightheadedness, nausea.
and headaches. Some effects have been observed at concentrations as low
as 300 ppm. These symptoms usually disappear quite rapidly after
exposure ends.
-------
2 Section I
Some of the effects to the nervous system caused by DCM may be
because of the breakdown of DCM In the body to carbon monoxide (CO)
Carbon monoxide Interferes with the blood's ability to carry oxygen (02)
to the tissues and causes symptoms similar to the narcotic effects
previously described. Since smoking Increases the amount of CO in the
blood, smokers may experience effects to the nervous system at lower
levels of DCM exposure than do nonsmokers.
The results of animal studies suggest that frequent or lengthy
exposures to DCM can cause changes in the liver and kidney. However,
based on these studies and those of exposed workers, it appears unlikely
that DCM will cause serious liver or kidney damage in humans unless
exposure is very high. No liver or kidney effects vere reported in
humans exposed to 30 to 125 ppm DCM in the workplace for up to 30 years.
or to 140 to 475 ppm for at least 3 months. In animal studies, mild
liver effects were observed from 100 ppm (100 days) to 3,500 ppm
(2 years). It should be noted that hepatic effects reported at 100 ppm
were elicited after continuous exposure without recovery as opposed to
the more traditional exposure protocol.
In certain laboratory experiments, animals exposed to high
concentrations of DCM throughout their lifetime developed cancer.
Methylene chloride has not been shown to cause cancer in humans exposed
at occupational levels; however, based on animal tests, it should be
treated as a potential cancer-causing substance.
1.5 IS THERE A MEDICAL TEST TO DETERMINE IF I
HAVE BEEN EXPOSED TO METHYLENE CHLORIDE?
Several methods exist for determining whether a person has recently
been exposed to DCM. Methylene chloride can be measured In the breath co
determine recent exposure; the amount of chemical detected will reflect
the amount inhaled. The urine can also be analyzed by monitoring for DCM
itself or for some intermediate products (such as formic acid) that are
produced as DCM breaks down in the body. Blood can be analyzed to
determine possible DCM exposure by monitoring blood levels of
carboxyhemoglobin (CO-Hb). Carbon monoxide formed in the blood through
the breakdown of DCM readily binds with hemoglobin to form CO-Hb. Thus,
excessive levels of CO-Hb in the blood can be an indication of exposure
to high concentrations of DCM. Although exposure to DCM can be monitored
through these sources, measurements determined have not provided
definitive quantitative information.
1.6 WHAT LEVELS OF EXPOSURE HAVE RESULTED IN
HARMFUL HEALTH EFFECTS?
The graphs on the following pages (Figs. 1.1 and 1.2) show the
relationship between exposure to DCM and known health effects. In the
first set of graphs labeled "Health effects from breathing methylene
chloride," exposure is measured In parts of chemical per million pares
of air (ppm). In all graphs, effects in animals are shown on the left
side and effects In humans on the right side.
-------
Public Health Statement
SHORT-TERM EXPOSURE
(LESS THAN OR EQUAL TO 14 DAYS)
LONG-TERM EXPOSURE
(GREATER THAN 14 DAYS)
EFFECTS
IN
ANIMALS
CONC IN
AIR
(ppm)
100.000
EFFECTS
IN
HUMANS
EFFECTS
IN
ANIMALS
CONC IN
AIR
(ppm)
100.000
DEATH
CNS EFFECTS •
EFFECTS
IN
HUMANS
QUANTITATIVE
DATA WERE NOT
AVAILABLE ON
EXPOSURE TO
DCM ALONE
10.000
10.000
LIVER TOXICITY •
CNS EFFECTS 1.000
1.000
•CNS EFFECTS
•CNS EFFECTS
100
LIVER TOXICITY •
100'
10
10
'Continuous exposure
Fig. 1.1. Health effects from breathing methylene chloride.
-------
Seed on 1
SHORT-TERM EXPOSURE
(LESS THAN OR EQUAL TO 14 DAYS)
LONG-TERM EXPOSURE
(GREATER THAN 14 DAYS)
EFFECTS
IN
ANIMALS
DOSE
(mg/kg/day)
QUANTITATIVE
DATA WERE
NOT
AVAILABLE
1000
EFFECTS
IN
HUMANS
QUANTITATIVE
DATA WERE
NOT
AVAILABLE
EFFECTS
IN
ANIMALS
DOSE
(mg/kg/day)
1000
100
LIVER TOXICITY
100
10
10
1 0
1 0
EFFECTS
IN
HUMANS
QUANTITATIVE
DATA WERE
NOT
AVAILABLE
Fig. 1.2. Health effects from ingesting methylene chloride.
-------
Public Health Statement 5
In the second set of graphs, the same relationship is represented
for the known "Health effects from eating or drinking products
containing methylene chloride." Exposures are measured in milligrams of
DCM per kilogram of body weight (mg/kg).
In case studies involving humans, the primary health effects are on
the central nervous system. Short exposures to concentrations of SOO ppm
(duration not specified) and above result in chemical intoxication,
tiredness, and irritability. One study reported a slight effect on
sensory function at 300 ppm (4 hours). At concentrations of 500 ppm
(duration not specified) and above, DCM also irritates the nose and
throat.
Rats have developed changes in liver cells following long-term
ingestion of 50 mg/kg/day DCM in drinking water. However, based on
animal and human studies, it appears unlikely that DCM will cause
serious liver effects in humans unless exposure is very high.
Methylene chloride is not known to cause cancer in humans, but
based on animal studies, the Environmental Protection Agency (EPA)
believes that DCM has the potential to cause cancer in humans. Exposures
should, therefore, be avoided or, when unavoidable, kept to the lowest
level feasible.
1.7 WHAT RECOMMENDATIONS HAS THE FEDERAL GOVERNMENT
MADE TO PROTECT HUMAN HEALTH?
The Occupational Health and Safety Administration (OSHA 1979) has
established exposure limits for persons who work with DCM. These include
an 8-hour time-weighted average (TWA) of 1,737 milligrams per cubic
meter (mg/m3) (500 ppm); an acceptable ceiling concentration of 3,474
mg/m3 (1,000 ppm); and an acceptable maximum peak above the ceiling of
6,948 mg/m3 (2,000 ppm) (5 minutes in any 2 hours) in the workplace air
OSHA is currently considering revising these standards based on the
recent information available on cancer studies in animals.
In 1976, the National Institute for Occupational Safety and Health
(NIOSH 1976) recommended a 10-hour TWA exposure limit of 261 mg/m3
(75 ppm) apd a 1,737 mg/m3 (500 ppm) peak (15-minute sampling) in the
presence of CO concentrations less than or equal to 9.9 ppm. These
recommendations were made because DCM and CO are responsible for the
same kinds of toxic effects. Lower levels of DCM are required in the
workplace when CO concentrations greater than 9.9 ppm are present.
Because DCM has been shown to induce increased numbers of benign and
malignant neoplasms in rats and mice, NIOSH currently recommends that
the compound be considered a potential human carcinogen in the workplace
and that the TWA exposure limit of 75 ppm be reduced to the lowest
feasible limit.
-------
2. HEALTH EFFECTS SUMMARY
2.1 INTRODUCTION
This section summarizes and graphs data on the health effects
concerning exposure to DCM. The purpose of this section is to present
levels of significant exposure for DCM based on key toxicological
studies, epidemiological investigations, and environmental exposure
data. The information presented in this section is critically evaluated
and discussed in Sect. 4, Toxicological Data, and Sect. 7, Potential for
Human Exposure.
This Health Effects Summary section comprises two major parts.
Levels of Significant Exposure (Sect. 2.2) presents brief narratives and
graphics for key studies in a manner that provides public health
officials, physicians, and other interested individuals and groups wich
(1) an overall perspective of the toxicology of DCM and (2) a summarized
depiction of significant exposure levels associated with various adverse
health effects. This section also includes information on the levels of
DCM that have been monitored in human fluids and tissues and information
about levels of DCM found in environmental media and their association
with human exposures.
The significance of the exposure levels shown on the graphs may
differ depending on the user's perspective. For example, physicians
concerned with the interpretation of overt clinical findings in exposed
persons or with the identification of persons with the potential to
develop such disease may be interested in levels of exposure associated
with frank effects (Frank Effect Level, FEL). Public health officials
and project managers concerned with response actions at Superfund sites
may want information on levels of exposure associated with more subtle
effects in humans or animals (Lowest-Observed-Adverse-Effect Level,
LOAEL) or exposure levels below which no adverse effects (No-Observed-
Adverse-Effect Level, NOAEL) have been observed. Estimates of levels
posing minimal risk to humans (Minimal Risk Levels) are of interest to
health professionals and citizens alike.
Adequacy of Database (Sect. 2.3) highlights the availability of key
studies on exposure to DCM in the scientific literature and displays
these data in three-dimensional graphs consistent with the format in
Sect. 2.2. The purpose of this section is to suggest where there might
be insufficient information to establish levels of significant human
exposure. These areas will be considered by the Agency for Toxic
Substances and Disease Registry (ATSDR), EPA, and the National
Toxicology Program (NTP) of the U.S. Public Health Service in order to
develop a research agenda for DCM.
-------
8 Section 2
2.2 LEVELS OF SIGNIFICANT HUNAN EXPOSURE
To help public health professionals address the needs of persons
living or working near hazardous waste sites, the toxicology data
summarized in this section are organized first by route of exposure--
inhalation, ingestion, and dermal--and then by toxicological end points
that are categorized into six general areas--lethality, systemic/target
organ toxicity, developmental toxicity, reproductive toxicity, genetic
toxicity, and carcinogenicity. The data are discussed in terms of three
exposure periods--acute, intermediate, and chronic.
Two kinds of graphs are used to depict the data. The first type is
a "thermometer" graph. It provides a graphical summary of the human and
animal toxicological end points (and levels of exposure) for each
exposure route for which data are available. The ordering of effects
does not reflect the exposure duration or species of animal tested. The
second kind of graph shows Levels of Significant Exposure (LSE) for each
route and exposure duration. The points on the graph showing NOAELs and
LOAELs reflect the actual doses (levels of exposure) used in the key
studies. No adjustments for exposure duration or intermittent exposure
protocol were made.
Adjustments reflecting the uncertainty of extrapolating animal data
to man, intraspecies variations, and differences between experimental vs
actual human exposure conditions were considered when estimates of
levels posing minimal risk to human health were made for noncancer end
points. These minimal risk levels were derived for the most sensitive
noncancer end point for each exposure duration by applying uncertainty
factors. These levels are shown on the graphs as a broken line starting
from the actual dose (level of exposure) and ending with a concave-
curved line at its terminus. Although methods have been established to
derive these minimal risk levels (Barnes et al. 1987), shortcomings
exist in the techniques that reduce the confidence in the projected
estimates. Also shown on the graphs under the cancer end point are low-
levels risks (10'4 to 10'7) reported by EPA. In addition, the actual
dose (level of exposure) associated with the tumor incidence is plotted.
2.2.1 Key Studies
Humans exposed to high concentrations of DCM for short time periods
may experience effects on the central nervous system. In case reports of
humans exposed to DCM through inhalation, the major effects noted were
narcosis, irritability, analgesia, and fatigue. Short-term exposure to
about 300 to 800 ppm resulted in impairment of the sensory and
psychomotor function (Winneke 1974).
Data on laboratory animals also indicate that DCM has a "depressive"
effect on the central nervous system. The lowest concentration reported
to cause effects was 1,000 ppm (Fodor and Winneke 1971). At this dose, the
sleep patterns of rats were affected. The no-effect level in this study
was established as 500 ppm. Acute inhalation exposures to high
concentrations (4,000 to 20,000 ppm) of DCM have produced symptoms of
central nervous system depression (including narcosis) in several other
species, including mice (Flury and Zernik 1931), guinea pigs (Weinstein
et al. 1972), and dogs (Weinstein ec al. 1972, Von Oettingen et al.
-------
Health Effects Summary 9
Liver effects caused by exposure Co DCM have been documented in
repeated exposure studies on laboratory animals. Mild cytoplasmic
vacuolization and/or fatty changes were observed in the liver of mice,
rats, dogs, and monkeys following inhalation exposure. These effects
were seen following exposure of rats and dogs to 25 to 100 ppm for 100
days Twenty-five ppm was a no-effect level for mice; 100 ppm was a no-
effect level for monkeys (Haun et al. 1972). Foci, or areas of altered
morphology, fatty change, or necrosis, were observed in the liver of
rats and mice following long-term exposure (2-year inhalation study).
Lowest-observed-effect levels ranged from 500 to 1,000 ppm 6 h/day 5
days/week in rats (Nitschke et al. 1982, NTP 1986). Five mg/kg/day was
an oral no-effect level in rats, and 185 mg/kg/day was an oral no-effect
level in mice (NCA 1982, 1983). Nonspecific degenerative and
regenerative changes were observed in the kidneys of rats exposed to 25
or 100 ppm continuously for 100 days (Haun et al. 1972).
Exposure to high concentrations of DCM can cause
carboxyhemoglobinemia, a condition resulting from carbon monoxide (CO)
interference with oxygen transport in the blood. Metabolism of DCM
produces CO, which readily binds with blood hemoglobin to form
carboxyhemoglobin (CO-Hb). The National Institute for Occupational
Safety and Health (NIOSH) has recommended that exposure to DCM should
not produce CO-Hb levels that exceed 5% (i.e., no more than 5% of the
blood's hemoglobin should be saturated with CO).
A study (Ott et al. 1983c) on workers exposed to DCM through their
jobs in a fiber-extrusion plant provided information on the relationship
between DCM exposure and CO-Hb buildup, both in smokers and nonsmokers.
Hemoglobin saturation following exposure to 200 ppm DCM was about 4% in
nonsmokers and 10% in smokers. In those exposed to 100 ppm, saturation
was 2% in nonsmokers and 6% in smokers. At 50 ppm, saturation was
slightly more than 4% in smokers but less than 1% in nonsmokers. Data
from this study indicate that exposures to DCM concentrations below 50
ppm are not likely to result in the buildup of CO-Hb above the NIOSH-
recommended limit of 5%, either in smokers or nonsmokers.
Recently conducted long-term studies clearly demonstrate that DCM
causes cancer in laboratory animals (NTP 1986). Mice exposed via
inhalation to high concentrations of DCM (2,000 or 4,000 ppm)
experienced a dramatic increase in liver and lung malignant tumors
compared with mice that were not exposed to DCM. Rats exposed via
inhalation to DCM (1,000, 2,000, or 4,000 ppm) developed mammary gland
tumors, but these tumors were benign. Methylene chloride as a cancer-
causing agent in humans has not been established. Studies of workers
exposed to DCM for several years have not recorded a significant
increase in cancer cases above the number of cases expected for
nonexposed workers. However, these occupational studies are not adequate
to rule out a risk of cancer to humans from DCM exposure, and this
chemical should be regarded as a possible carcinogen in humans.
The primary adverse health effects associated with exposure to DCM
are depression of the central nervous system and mild liver toxicity.
These effects are summarized in Tables 2.1 and 2.2, and data from these
studies are presented graphically in Figs. 2.1 through 2.4.
-------
10 Section 2
Table 2.1. Key dose response data for short-term CNS effects
of methylene chloride
Route of
exposure Species
Inhalation Human
Inhalation Human
Rat
Dose-duration
LOAEL" -
(4h)
NOAEL* =
LOAEL =
LOAEL =
NOAEL =-
(24 h)
300-800 ppm
1 500 ppm
1,000 ppm
1,000-3,000 ppm
500 ppm
Effect
Impairment of
visual, auditory,
and psychomotor
functions
Decreased visual
function
Reduction in
sleeping time
References
Winneke 1974
Stewart et al.
1972
Fodor and
Winneke 1971
Oral
Dermal
No data available
on humans and
animals
No data available
on humans and
animals
• LOAEL •" lowest-observed-adverse-effect level.
* NOAEL = no-observed-adverse-effect level.
-------
Healch Effects Summary 11
Table 2.2. Key dote response data for long-term
bepatotoxkity effects of metbylene chloride
Route of
exposure Species
Dose-response
Effect
References
Inhalation
Inhalation
Inhalation
Inhalation
Mouse
Monkey
Rat
Dog
Rat
Rat
Rat
NOAEL - 25 ppm
LOAEL - 100 ppm
(100 days)
NOAEL - 100 ppm
LOAEL - 1,000 ppm
(100 days)
LOAEL - 25 ppm
(100 days)
NOAEL - 200 ppm
LOAEL - 500 ppm
(2 years)
LOAEL - 1. 000 ppm
(2 years)
LOAEL - 500-3.500 ppm
(2 years)
Histopathological
changes in liver.
including vacuoli-
zation and increased
fat content Weight
reduction in mice.
Multmucleated
hepatocytes
Increased
hemosiderosu*
cytomegaly. and
cytoplasm ic
vacuoluation
Multmucleated
hepatocytes with
cytoplasmic
vacuolization.
hemosiderosis, and
focal necrosis
Haun et al
1972
Nitschke et al.
1982
NTP 1986
Burek et al.
1980, 1984
Oral
(drinking
water)
Oral
(drinking
water)
Oral
Denial
Human
Rat
Mouse
Human
Cases of occupational
exposure were presented.
but dose-response
relationships were not
defined
NOAEL - 5 rag/kg/day
LOAEL - 50-250 mg/kg/day
(2 yean)
NOAEL - 185 mg/kg/day
LOAEL - 250 mg/kg/day
Histomorpnological
alterations in
liver
Fatty changes in
the liver
No data available
No data available
on humans or
animals
NCA 1982
NCA 1983
-------
12 Section 2
ANIMALS
10.000 r— • MICE CNS EFFECTS
• GUINEA PIGS CNS EFFECTS
• DOGS CNS EFFECTS
1000
100
10 *-
HUMANS
(PP"i)
10000 i—
f RATS. CNS EFFECTS. 24 h
- •< RATS. UVER EFFECTS. 2 YEARS
I MONKEYS. UVER EFFECTS. 100 DAYS
(• RATS LIVER EFFECTS. 2 YEARS
IJi RATS. CNS EFFECTS. 100 DAYS
' MICE LIVER TOXICITY. 100 DAYS
• RATS. KIDNEY EFFECTS. 100 DAYS
> MONKEYS. LIVER EFFECTS. 100 DAYS
!• RATS. KIDNEY EFFECTS. 100 DAYS
J« RATS. DOGS LIVER EFFECTS, 100 DAYS
(p MICE LIVER TOXICITY. 100 DAYS
1000
100
• LOAEL FOR ANIMALS
O NOAEL FOR ANIMALS
A LOAEL FOR HUMANS
A NOAEL FOR HUMANS
10 •—
A CNS EFFECTS 5 h
£ UVER LUNG
(>20 YEARS)
'Continuous exposure
Fig. 2.1. Effects of methylene chloride—inhalation exposure.
-------
Health Effects Summary 13
(ppm)
10.000
1 000
100
10
1 0
01
001
0001 -
00001 -
0 00001 «-
ACUTE
(<14 DAYS)
TARGET
ORGAN
• m (CMS)
• g(CNS)
•d (CMS)
•r (CNS)
INTERMEDIATE
(15-364 DAYS)
CHRONIC
(>365 DAYS)
TARGET
ORGAN
REPRO-
DUCTION
TARGET
ORGAN
CANCER
f (CNS)
m(LIVER)
I
k (LIVER)
I
r (LIVER)
• r (KIDNEY. LIVER)
d (LIVER)
10-5-
10-6-
ESTIMATED
UPPER-BOUND
HUMAN
CANCER
RISK LEVELS
r RAT
m MOUSE
k MONKEY
d DOG
g GUINEA PIG
A LOAEL FOR HUMANS
• LOAEL FOR ANIMALS
O NOAEL FOR ANIMALS
I
I MINIMAL RISK LEVEL FOR
I EFFECTS OTHER THAN
\llCANCER
Fig. 2.2. Levels of significant exponrc for nettaylene chloride—inhaladoo.
-------
14 Seccion 2
ANIMALS
(mg/kg/day)
1000 i—
HUMANS
100
• MOUSE. LIVER EFFECTS. 2 YEARS
O MOUSE LIVER EFFECTS. 2 YEARS
RAT. LIVER EFFECTS. 2 YEARS
10
O RAT. LIVER EFFECTS. 2 YEARS
10 L-
• LOAEL
ONOAEL
QUANTITATIVE DATA
WERE NOT AVAILABLE
Fig. 2J. Effects of methylene chloride—oral exposure.
-------
Health Effects Siunmary 15
(mg/kg/day)
LOOOr-
100
10
0.1
0.01
0.001
00001
0.00001 !-
ACUTE INTERMEDIATE
(S14 DAYS) (15-364 DAYS)
LETHALITY
• r
m MOUSE
r RAT
QUANTITATIVE
DATA WERE NOT
AVAILABLE
• LOAEL
O NOAEL
CHRONIC
(>365 DAYS)
TARGET
ORGAN
• m (LIVER)
O
r (LIVER)
CANCER
• m
10-4-,
10-5-
10
-7-
ESTIMATED
UPPER-BOUND
HUMAN
CANCER
RISK LEVELS
MINIMAL RISK LEVEL
FOR EFFECTS OTHER
THAN CANCER
Fig. 2.4. Levcb of significant exposure for methykM chloride—onL
-------
16 Section 2
2.2.1.L Lethality
Inhalation, human. Case reports (Bonventre et al. 1977, Stewart
and Hake 1976) have implicated exposure to exceedingly high levels of
DCM as a factor in human fatalities. However, exposure levels and
durations are not known, and simultaneous exposure to unspecified
chemicals was often the case.
Inhalation, animal. Studies demonstrate that DCM is lethal in
laboratory animals via inhalation. Inhalation LC50 values of 11,000 to
16,000 ppm (for 6 to 8 h) have been reported (EPA 1985c) (Table 4.2).
Oral, human. No lethality studies were found in the available
literature on the oral administration of DCM in humans.
Oral, animal. Oral LD50 values of 1,000 to 2,000 mg/kg have been
reported (EPA 1985c) (Table 4.1).
Oral, dermal. No lethality studies were found in the available
literature on the dermal administration of DCM in humans and animals.
2.2.1.2 Systemic/target organ toxicity
Central nervous system, inhalation (human). The major
manifestation in humans of short-term exposure to DCM is the impairment
in the functioning of the central nervous system. Winneke (1974) used
indicators of behavioral performance to study the effects of DCM on the
nervous system. Human volunteers were exposed to DCM via inhalation at
average concentrations of 0, 317, 470, or 751 ppm for up to 4 h.
Decreased visual and auditory functions were observed at 300 ppm or
above, and decreased performance in most psychomotor tasks was
demonstrated in groups subjected to 751 ppm compared with untreated
controls. A second study (Stewart et al. 1972) reported impairment of
the central nervous system (CNS) in two of three test subjects who
inhaled vapors of DCM (1,000 ppm) for 1 to 2 h. The subjects
demonstrated a reduced ability to respond to stimuli. A concentration of
500 ppm for a corresponding exposure duration was without effect.
Central nervous system. Inhalation (animal). There are few studies
on the effects of DCM on the CNS apart from experiments that quantify
the anesthetic response. The percentage of sleeping time characterized
by rapid eye movements was reduced in rats following exposure to 1,000
ppm for 24 h (Fodor and Winneke 1971). At 5,000 to 9,000 ppm, long
sleeping periods occurred without the desynchronization phases that
usually appear every few moments in normal sleep (Berger and Fodor
1968). Exposure to 5,000 ppm has been shown to reduce the spontaneous
running activity of rats (Heppel et al. 1944).
Central nervous system, inhalation (oral and dermal). No studies
were found in the available literature on humans and animals.
Hepatotozicity, inhalation (human). No data were found in the
available literature on acute DCM-Induced hepatotoxicity in humans.
Long-term studies involving occupational exposures did suggest
qualitatively that DCM may cause liver toxicity, as evidenced by a
reported case of hepatitis and altered triglyceride levels. The
importance of these responses is reduced since no supporting
quantitative data were provided.
-------
Health Effaces Summary 17
Hepatotozicity, Inhalation (animal). Structural and biochemical
changes in the liver have been reported following short- and long-term
inhalation exposure to DCM. Cytoplasmic vacuolization and/or fatty
changes were observed in the livers of mice, rats, dogs, and monkeys
following continuous inhalation exposures in the range of 25 to
1.000 ppm for 100 days (Haun 1972). Rats and dogs showed mild effects at
concentrations as low as 25 ppm; mice exhibited fat accumulation and
glycogen depletion at continuous exposure to 100 ppm, and microscopic
examination of the livers of monkeys exposed to 1,000 ppm showed mild
fatty degeneration. Further, fatty changes were also observed in dogs
continuously exposed to DCM (5,000 ppm) for 25 h (HacEwen et al. 1972)
and in mice at 5,200 ppm for 6 h (Morris et al. 1979).
Rats were exposed to DCM via inhalation for 2 years at
concentrations of 50, 200, and 500 ppm (Nitschke et al. 1982, 1988), or
at 500, 1,500, and 3,500 ppm (Burek et al. 1980. 1984). Hepatic
vacuolization was noted in both sexes at 500 ppm. The incidence of
multinuclear hepatocytes was also increased in females at exposures
greater than 500 ppm. Higher exposure levels resulted in increased
numbers of foci, or areas of altered hepatocytes (at 3,500 ppm in
females), and necrosis (at 1,500 ppm in males and 3,500 ppm in females).
A third study (NTP 1986) reported hemosiderosis, hepatomegaly,
cytoplasmic vacuolization, and focal necrosis at all test doses in rats
of both sexes exposed to 1,000, 2,000, and 4,000 ppm DCM for 2 years. In
studies with mice (NTP 1986), hepatic cytologic degeneration was
apparent at 4,000 ppm in both sexes and at 2,000 ppm in females.
Hepatotozicity, oral (human). No hepatotoxicity studies were found
in the available literature on the oral administration of DCM in humans.
Hepatotozicity. oral (animal). No data were found in the available
literature on the histomorphological effects of DCM in the liver
following acute oral exposure. There is, however, some evidence for
biochemical changes. The microsomal cytochrome P-450 content in rats was
reduced 18 h after being dosed with 1 g/kg DCM (Moody et al. 1981).
Increased triglyceride content, reduced triglyceride secretion, and
reduced tubulin protein content were reported for mice given 2.7 g/kg
DCM.
Prolonged exposure to DCM produced mild toxic effects in the liver.
The National Coffee Association (NCA 1982) evaluated the chronic
toxicity of DCM ingested by F344 rats (50/sex/dose) in drinking water at
target doses of 0, 5, 50, 125, or 250 mg/kg/day for 104 weeks.
Additional high-dose (250 mg/kg/day) groups (25 animals/sex) were
administered DCM for 78 weeks and then allowed to recover for a period
of 26 weeks. Hepatic histological alterations, including increased
incidence of foci (areas of cellular alterations), were detected at 78
weeks and at 104 weeks of treatment in the 50-, 125-, and 250-mgAg/day
dose groups for both sexes. Fatty liver changes occurred in rats of both
sexes given 125 and 250 mg/kg/day. A no-effect level of 5 mg/kg/day was
determined. Male and female B6C3F1 mice exposed to 0, 60, 125, 185, or
250 mg/kg/day of DCM in their drinking water for 2 years exhibited liver
effects only at the highest dose (NCA 1983). A slight increase in the
incidence of foci of altered morphology (hepatocellular hyperplasia)
occurred in treated males, but the effect was not statistically
-------
18 Section 2
significant; the number of animals with this effect was within the
normal variation for this strain of mouse. An increased amount of fatty
change occurred in mice given 250 mg/kg/day. A no-effect level of 185
mg/kg/day was determined.
Hepatotoxicity. oral (dermal). No hepatotoxicity studies were
found in the available literature on the dermal administration of DCM in
humans and animals.
Renal effects, inhalation (human). No association between DCM
exposure and adverse effects on the kidney were reported in several
epidemiologic studies (Friedlander et al. 1978, Ott et al. 1983, Hearne
et al. 1987).
Renal effects, inhalation (animal). Continuous exposure to DCM (25
and 100 ppm) for 100 days showed nonspecific renal tubular degenerative
and regenerative changes in rats; however, there were no changes in the
organ-body weight ratio. A NOAEL of 100 ppm for 100 days was determined
for the dog (Haun et al. 1972).
Renal effects, inhalation (oral and dermal). No studies were found
in the available literature on renal toxicity following the oral and
dermal administration of DCM in humans and animals.
2.2.1.3 Developmental toxicity
No data were found in the available literature on the effects of
DCM in humans following inhalation, oral, or dermal exposure. Animal
data demonstrated that inhalation of DCM at dose levels of 1,250 ppm
produced a minor skeletal variant (extra sternebrae, P < 0.05) in mice
(Schwetz et al. 1975). Fetus weight was reduced, and behavioral changes
occurred in rat pups following exposure of dams to 4,500 ppm DCM (Hardin
and Manson 1980). The practical importance of these findings is limited.
since each of the two studies used only one dose level and the observed
effects occurred at maternally toxic doses. Evidence, therefore, does
not currently exist to conclusively characterize the developmentally
toxic potential of DCM in humans.
2.2.1.4 Genotoxicity
Methylene chloride has been evaluated in a variety of short-term
mammalian systems in vitro and in vivo to assess its potential to induce
gene mutation and cause chromosomal aberrations and DNA/damage and
repair (I11ing and Shlllaker 1985, CEFIC 1986d). Methylene chloride has
been shown to cause mutations in in-vitro test systems employing
bacteria or yeast. Results were generally negative in vivo. Overall, DCM
appears to be a weak mutagen in lower species, but evidence of
mutagenicity in mammalian cells is lacking.
2.2.1.5 Reproductive toxicity
Methylene chloride did not adversely affect reproduction in rats
exposed to 0. 100, 500, or 1,500 ppm via inhalation for two generations
(Nitschke et al. 1985, unpublished).
-------
Health Effaces Summary 19
2.2.1.6 Carcinogenicity
Inhalation, human. Epidemiologies! studies have not demonstrated a
significant increase in cancer deaths Ln humans occupationally exposed
to DCM. The results of studies of deaths in male workers exposed to TWA
concentrations (30 to 125 ppm) for up to 30 years showed no excess liver
or lung cancer mortality (Frledlander et al. 1978). No excess deaths
from lung and liver cancer were reported in a study evaluating the
mortality experiences of an expanded cohort exposed at a rate of 26 ppm
(8-h TWA) for 22 years (median latency of 30 years) (Hearne et al.
1987). However, an elevated incidence of pancreatic cancer deaths was
reported in the Hearne et al. 1987 study. These deaths were not
considered to be statistically significant. Ott et al. (1983a) evaluated
cancer mortality among employees of a fiber production plant who were
exposed to TWA concentrations of 140 to 475 ppm. They observed fewer
than expected deaths from malignant neoplasms in comparison to expected
deaths from the same cause in the general population.
Although the available human evidence suggested that DCM is not
carcinogenic at levels of exposure in an occupational setting of up to
475 ppm, these epidemiological studies were inadequate and cannot rule
out the possibility of some risk associated with exposure to DCM. Based
on animal studies, EPA considers DCM to be a probable human carcinogen
(EPA 1987b).
Inhalation, animal. Methylene chloride induced a dose-dependent,
statistically significant increase in liver and lung adenomas and
carcinomas in male and female mice exposed via inhalation for a lifetime
at concentrations of 2,000 or 4,000 ppm (NTP 1986). Tumor incidences
were as follows: at 2,000 ppm, 30 of 48 female mice and 27 of 50 male
mice developed lung tumors compared with 3 of 50 female mice and 5 of 50
male mice in controls. Female mice (16 of 48) and male mice (24 of 49)
also developed liver tumors. At 4,000 ppm, 41 of 48 female mice and 40
of 50 male mice developed lung tumors; 40 of 48 female mice and 33 of 49
male mice developed liver tumors. In controls, liver tumors developed in
3 of 50 female mice and in 22 of 50 male mice.
In a rat bioassay (NTP 1986), DCM induced a statistically
significant increase in benign mammary tumors, of a type not expected to
progress into malignant tumors (McConnell et al. 1986), in female rats
exposed at 2,000 or 4,000 ppm. Male rats developed mammary gland
fibroadenomas at 4,000 ppm, but only at a marginally significant rate.
The NTP interpreted its study as showing clear evidence of animal
carcinogenicity.
Oral, human. No carcinogenicity studies were found in the
available literature on oral administration in humans.
Oral, animal. A carcinogenic effect has been demonstrated in
laboratory animals following long-term oral exposure to DCM. The
National Coffee Association (NCA) evaluated the carcinogenic potential
of DCM in rats and mice. In the rat study (NCA 1982), DCM (at doses of
0, 5, 50, 125, and 250 mgAg/day) was administered in drinking water to
Fischer 344 rats of both sexes for 104 weeks. An increase in liver
tumors, which was within historical control incidences, was noted in
females treated at 50 and 250 mg/kg/day when compared to concurrent
-------
20 Section 2
controls. The authors did not consider these effects to be attributed to
DCM treatment, since there was an unusually low incidence of similar
tumors in the concurrent control groups and an absence of increased
incidence of hepatic tumors in the group treated at 125 mg/kg/day. The
EPA (1985a) evaluated the results of this study and reported an
increased incidence of neoplastic nodules combined with hepatocellular
carcinomas in female rats (P < 0.05) when compared with matched
controls. Tumor incidences were as follows: 0/134, 1/85, 4/83, 1/85, and
6/85 in combined control, 5-, 50-, 125-, and 250-mg/kg/day groups,
respectively. The EPA (1985a) concluded that based on the combined
incidence of adenomas and carcinomas, DCM showed borderline evidence of
careinogenieity in rats when administered orally.
In the mouse study (NCA 1983), DCM was administered in drinking
water at doses of 0, 60-, 125-, 185-, and 250-mgAg/day for 104 weeks. A
slight increase (not statistically significant) in proliferative
hepatocellular lesions was reported in treated male groups when compared
with male controls (but not in females). The authors concluded that DCM
was not carcinogenic under conditions of this study, since the tumor
incidences were not dose related and were within historical control
levels. An EPA (1985b) assessment of the mouse study reported a
marginally significant (P < 0.05) increase in the combined incidence of
hepatocellular adenoma and carcinoma in male mice (24/125, 51/200,
30/100, 31/99, and 35/125 in combined control, 60-, 125-, 185-, and
250-mgAg/day groups, respectively). The EPA (1985b) considers the
evidence for the carcinogenicity of DCM in mice via oral exposure to be
borderline.
2.2.1.7 Mechanisms of action
The primary effect produced following DCM exposure was impairment
of the CNS. Methylene chloride also affected the cardiovascular system,
the liver and kidneys, was mutagenic in bacteria and yeast, and produced
tumors in laboratory animals. Adverse effects produced following DCM
exposure may be due to the parent compound, its reactive intermediates,
or a combination of these.
The CNS toxicity of DCM may be attributable to direct central
depressant action, since DCM is a known anesthetic agent. This effect
would be expected to be important if high-level exposures were
encountered. Methylene chloride undergoes metabolism to reactive
intermediates which become irreversibly bound to tissue protein and
lipids. The relationship between this bioactivation and the fatty liver
produced by DCM is not clear, but metabolism appears to be involved in
the mutagenic effect of DCM seen in bacteria and yeast. The CNS toxic icy
of DCM may also be associated with the carbon monoxide produced as a
metabolite of DCM. Carbon monoxide may be potentially dangerous in
individuals with cardiovascular disease, and may contribute to deficits
in human performance detected by behavioral testing following DCM
exposure.
Based on studies in mice. DCM's carcinogenicity is most likely
produced as a result of metabolism via the glutathione conjugation
[glutathione-S-transferase (GST)] pathway. Parent DCM and the oxidation
-------
Health Effects Summary 21
[mixed-function oxidases (MFO)] pathway are considered to be possible
sources of tumorigenic potential rather than probable sources. Neither
the parent nor the oxidation pathway correlates with tumor incidence,
either among species or across doses.
Current evidence is not sufficient to identify with reasonable
certainty the carcinogenic mechanism of action of DCM. Genotoxicity and
cytotoxicity have been investigated; however, neither has been clearly
shown to be the cause of carcinogenicity seen in animal studies.
Additional data on the mechanism of action may be provided by the
National Institute of Environmental Health Science (NIEHS), which plans
to investigate further the role of cell replication in DCM tumorigenesis
and the pattern of oncogene activation in spontaneous and dose-related
tumors. Also, the European Center of Chemical Manufacturers' Federation
(CEFIC) is conducting studies to evaluate the effects of DCM in Clara
cells in relation to tumor development.
2.2.2 Biological Monitoring as a Measure of Exposure and Effects
Methylene chloride exposure may be monitored by its determination
in the blood, breath, or urine of exposed persons (NIOSH 1976).
Methylene chloride and formic acid were found in measurable amounts
in the urine of persons exposed to the chemical. The amount of DCM found
in a 24-h period following a 24-h exposure at 100 and 200 ppm was
proportional to the exposure concentrations (DiVincenzo et al. 1972).
Formic acid was found in the urine of most persons exposed to DCM in a
particular occupational study, but no correlation between the intensity
of exposure and the concentration of formic acid could be determined
(Kuzelova and Vlasak 1966).
Methylene chloride has also been measured in the blood and breath
of exposed persons. The concentrations of DCM in the blood and breath
have been representative of the exposure (Astrand et al. 1975, Riley et
al. 1966, DiVincenzo et al. 1972).
Carboxyhemoglobin (CO-Hb) in persons exposed to DCM at rest is
dependent on the exposure concentration, duration, and the extent of
concurrent carbon monoxide exposure. These relationships, however, are
disrupted by physical activity. With increased activity, maximum CO-Hb
values may not be attained until 3 to 4 h after the end of the exposure.
Although it is possible to monitor CO-Hb levels in workers exposed to
DCM, the time that the measurements should be made in relation to the
end of exposure has not been well established. Consequently, a series of
measurements may prove more informative. Since the relationship between
alveolar carbon monoxide and CO-Hb has not been well established for DCM
workers, breath analysis for carbon monoxide cannot be considered as
providing definitive quantitative information regarding DCM exposure.
2.2.3 Environmental Levels as Indicators of Exposure and Effects
2.2.3.1 Levels found in the environment
Methylene chloride has been detected in ambient air, in surface and
drinking water, and at very low levels in decaffeinated coffee and
spices. However, these sources of exposure are considered to be minor.
-------
22 Section 2
Mechylene chloride occurs in ambient air with levels in the parts-per-
trillion range and has been detected only at low levels (7 mg/L was the
maximum level) in surface and drinking water (EPA 1980). The U.S. Food
and Drug Administration reports that DCM levels in decaffeinated coffee
and spices are extremely low. Methylene chloride is also formed from
natural sources; however, natural sources are not considered as
significant contributors to environmental concentrations (EPA 1980).
2.2.3.2 Human exposure potential
Exposures to DCM occur primarily in workplaces that use DCM and
also through the use of DCM consumer products. Exposure to DCM in
outdoor air, water, and food is low.
2.3 ADEQUACY OF DATABASE
2.3.1 Introduction
Section 110 (3) of SARA directs the Administrator of ATSDR to
prepare a toxicological profile for each of the 100 most significant
hazardous substances found at facilities on the CERCLA National
Priorities List. Each profile must include the following content:
"(A) An examination, summary, and interpretation of available
toxicological information and epidemiologic evaluations on a
hazardous substance in order to ascertain the levels of
significant human exposure for the substance and the
associated acute, subacute, and chronic health effects.
(B) A determination of whether adequate information on the health
effects of each substance is available or in the process of
development to determine levels of exposure which present a
significant risk to human health of acute, subacute, and
chronic health effects.
(C) Where appropriate, an identification of toxicological testing
needed to identify the types or levels of exposure that may
present significant risk of adverse health effects in humans."
Thia section identifies gaps in current knowledge relevant to
developing levels of significant exposure for DCM. Such gaps are
identified for certain health effect end points (lethality,
systemic/target organ toxicity, developmental toxicity, reproductive
toxiclty, and carcinogenicity) reviewed In Sect. 2.2 of this profile in
developing levels of significant exposure for DCM. and for other areas
such as human biological monitoring and mechanisms of toxicity. The
present section briefly summarizes the availability of existing human
and animal data, identifies data gaps, and summarizes research in
progress that may fill such gaps.
Specific research programs for obtaining the data needed to develop
levels of significant exposure for DCM will be developed by ATSDR, NTP,
and EPA in the future.
-------
Health Effects Summary 23
2.3.2 Health Effect End Points
2.3.2.1 Introduction and graphic summary
Because DCH Is found in consumer products such as insecticides,
metal cleaners, paints, and paint varnish removers, and occurs in water,
numerous evaluations have been conducted to assess its potential as a
human health hazard. The availability of data for health effects in
humans and animals is depicted on bar graphs in Figs. 2.5 and 2.6,
respectively.
The bars of full height indicate that there are data to meet at
least one of the following criteria:
1. For noncancer health end points, one or more studies are available
that meet current scientific standards and are sufficient to define
a range of toxicity from no-effect levels (NOAELs) to levels that
cause effects (LOAELs or FELs).
2. For human carcinogencity, a substance is classified as either a
"known human carcinogen" or "probable human carcinogen" by both EPA
and International Agency for Research on Cancer (IARC)
(qualitative), and the data are sufficient to derive a cancer
potency factor (quantitative).
3. For animal carcinogenicity, a substance causes a statistically
significant number of tumors in at least one species, and the data
are sufficient to derive a cancer potency factor.
4. There are studies which show that the chemical does not cause this
health effect via this exposure route.
Bars of half height indicate that "some" information for the end
point exists but does not meet any of these criteria.
The absence of a column indicates that no information exists for
that end point and route.
2.3.2.2 Description of highlights of graphs
Most of the studies in the available literature are for inhalation
exposure; an exception is a 2-year drinking water study with rodents.
Systemic effects have been adequately evaluated in animals; similarly,
such effects have been observed in humans, but the reported findings
were not supported by quantitative and histomorphological data.
2.3.2.3 Suaaary of relevant ongoing research
Several studies are in progress that would contribute new and
useful Information on DCM toxicity. These studies include the following
• Role of cell replication in DCM tumorigenesis and the pattern of
oncogene activation in spontaneous and dose-related tumors (by
NIEHS).
• Liver cell turnover as a mechanism of carcinogenesis in mouse liver
(by CEFIC).
-------
HUMAN DATA
ro
-P-
ZIZ
J
SUFFICIENT
'INFORMATION*
J
SOME
INFORMATION
NO
INFORMATION
ORAL
INHALATION
DERMAL
LETHALITY ACUTE INTERMEDIATE CHRONIC DEVELOPMENTAL REPRODUCTIVE CARCINOOENICITY
ZL _ y TOXICITY TOXICITY
SYSTEMIC TOXICITY
'Sufficient information exists to meet at least one of the criteria for cancer or noncancer end points.
Fig. 2.5. Avuiliibilily of information on health effects of melhylene chloride (human data).
-------
ANIMAL DATA
v SUFFICIENT
"INFORMATION*
J
. SOME
INFORMATION
NO
INFORMATION
ORAL
INHALATION
DERMAL
LETHALITY ACUTE INTERMEDIATE CHRONIC DEVELOPMENTAL REPRODUCTIVE CARCINOOENICITY
/ / TOXICITY TOXICITY
3
m
n
PI
in
fVSTEMIC TOXICITY
'Sufficient information exists to meet at least one of the criteria for cancer or noncancer end points.
Kig. 2.6. Availability of information on health effects of methylene chloride (animal data).
ro
t-n
-------
26 Section 2
• Glutathione pathway rates from the 36C1 isotope (by Dow Chemical
Company and CEFIC).
• Measurements of new partition coefficients (by CEFIC).
• In vivo pathway measurements with deuterated DCM (by CEFIC).
These studies will help elucidate the mechanism of action of DCM
and will improve knowledge of species differences in pharmacokinetics.
2.3.3 Other Information Needed for Human Health Assessment
2.3.3.1 Pharmacokinetics and mechanisms of action
The pharmacokinetics of DCM have been extensively studied. Based on
these studies, two metabolic pathways are known: one involving
glutathione-S-transferase (GST) and the other involving oxidation
mixed-function oxidase (MFO). The GST pathway is believed to produce
carbon dioxide (C02), whereas the MFO pathway produces CO and C02.
The current evidence is not sufficient to identify with reasonable
certainty the mechanism of action of DCM. Based on studies in rodents
(mice), DCM's carcinogenicity is believed to be the result of metabolism
via the GST pathway. Both pathways may be active in mice at low doses,
but at higher doses the MFO pathway becomes saturated, and the metabolic
load is increasingly shifted to the alternative GST pathway. Parent DCM
and the MFO pathway are considered to be possible sources of tumorigenic
potential rather than probable sources. Neither one correlates with
tumor incidence, either among species or across doses. Further, the
parent compound is thought to be chemically unreactive. Much uncertainty
exists about the mechanism of action of DCM. -The genotoxicity and
cytotoxicity of DCM have been investigated as possible mechanisms of
carcinogenic action, but neither has been shown definitively to be the
cause for the tumorigenicity observed in animal studies. Additional data
on mechanisms are needed. The NIEHS is investigating the role of cell
replication in DCM tumorigenesis and the pattern of oncogene activation
in spontaneous and dose-related tumors. The CEFIC is conducting studies
to evaluate the effects of DCM in the Clara cell in relation to lung
tumor development. Methylene chloride produces liver and kidney effects
in laboratory animals; however, the mechanism by which these effects are
produced is not known. The CNS effects produced following exposure to
DCM are probably due to DCM alone or in combination with CO-Hb.
2.3.3.2 Monitoring of human biological samples
Several methods are used to test human exposure to DCM. The
analysis of DCM in breath is a good indicator of exposure since most of
the DCM taken Into the body is eliminated unchanged In expired air from
the lungs. Analysis of the blood and urine can also be used to determine
exposure to DCM in humans.
2.3.3.3 Environmental considerations
Current methodologies to assess the levels of DCM in the
environment are adequate. However, there is an absence of adequate data
on exposure from the ambient environment.
-------
27
3. PHYSICAL AND CHEMICAL INFORMATION
3.1 CHEMICAL IDENTITY
The chemical formula, structure, synonyms, trade names, and
Identification numbers for DCM are listed in Table 3.1.
3.2 PHYSICAL AND CHEMICAL PROPERTIES
Important physical and chemical properties of DCM are listed in
Table 3.2.
-------
28
Section 3
Table 3.1. Chemical identity of methylene chloride
Chemical name
Synonyms
Trade names
Chemical formula
Wiswesser line notation
Chemical structure
Identification numbers:
CAS Registry No.
NIOSH RTECS No.
EPA hazardous waste No.
OHM-TADS No.
DOT/UN/NA/IMCO Shipping No.
STCC No.
Hazardous Substances Data Bank No.
National Cancer Institute No.
Methylene chloride
Dichloromethane
DCM
Methane dichlonde
Methane, dichloro (8CI and 9CI)
Methylene bichloride
Methylene dichlonde
Aerothene MM
Freon 30
Narkotil
R30
Solaesthin
Solmethme
CH2C12
GIG
Cl
H-C-H
l
Cl
75-09-2
PA8050000
U080, F002
7217234
UN 1593
66
C50102
Source: HSDB 1987.
-------
Chemical and Physical Information 29
Table 3.2. Physical and chemical properties of methylene chloride
Property
Molecular weight
Color
Physical state
Odor
Odor threshold
Melting point
Boiling point
Autoignition temperature
Solubility
Water (20 to 30° C)
Organic solvents
Value
84.93
Colorless
Liquid
Characteristic,
sweetish, not
unpleasant
1 50-600 ppm
-95.1°C
40° C (at 760 mm Hg)
1,033°F
20,000 mg/L
Miscible with a wide
References
Weast 1985
Verschueren 1977
Verschueren 1977
Verschueren 1977
Ruth 1986
Weast 1985
Weast 1985
NFPA 1984
EPA 1986a
EPA I985c
Density at 20° C
Vapor density, air = 1
Partition coefficients
Octanol-water (Kg,,) log
Organic carbon (£«)
Vapor pressure (20 and 30° C)
Henry's law constant
Refractive index (20°C)
Flash point (closed cup)
Flammable limits
variety of organic
solvents
1.3266 g/mL
2.93
Weast 1985
Verschueren 1977
Conv
factors
1.30 EPA 1986a
8.8 g/mL EPA 1986a
349 and 500 mm Hg EPA 1986a
2.03 X 1CT3 atm-mVrnol EPA 1986a
1.4242 Weast 1985
Practically nonflammable NFPA 1984
14-22% NFPA 1984
1 ppm = 3.53 mg/m3 Verschueren 1977
in air
-------
31
A. TOXICOLOGICAL DATA
4.1 OVERVIEW
Mechylene chloride is a volatile liquid with high lipid solubility
and modest solubility in water. It is absorbed primarily by inhalation
and ingestion. Dermal exposure has resulted in DCM absorption in
laboratory animals and humans, but this occurs at a slower rate than
when administration is by other routes. Consistent with the properties
of high lipid solubility and modest water solubility, adsorption of DCM
following inhalation and ingestion is rapid. Once absorbed, DCM is
quickly distributed to a wide range of tissues and body fluids.
Methylene chloride is metabolized via two pathways, the MFC and the GST.
The GST pathway produces C02, whereas the HFO pathway produces CO and
C02. Methylene chloride is almost exclusively metabolized by the MFO
pathway at low exposures.
Acute exposure to DCM has been associated with impairment in
function of the central nervous system and liver and kidney effects. In
human experimental studies, DCM (330 ppm) decreased visual and auditory
functions and impaired psychomotor tasks (800 ppm) following inhalation
exposure for 5 h. Reduced sleeping time was reported in rats exposed to
DCM (1,000 ppm) for 24 h.
Subchronic exposure to DCM resulted in mild liver and kidney
effects in animals. Vacuolization and fatty changes in liver cells were
reported in mice, rats, and dogs that inhaled DCM (100 ppm) for 100
days. Degenerative and regenerative changes in kidney tubules were also
reported in rats exposed via inhalation to DCM (25 or 100 ppm) for 100
days. It should be noted that liver and kidney effects were elicited
after continuous exposure without recovery as opposed to the more
traditional exposure protocol.
Chronic exposure to DCM has been associated with mild liver
toxicity, as evidenced by cytoplasmic vacuolization, increased fat
content, and multinucleated hepatocytes following inhalation exposure at
>SOO ppm for 2 years. Histomorphological alterations and fatty changes
were also noted in mice and rats following oral exposure for 2 years.
Liver tumors were produced in rats and mice exposed to DCM in
drinking water for 2 years; however, the tumor incidences were not
considered by the study authors to be compound related since the
incidences were within historical control levels. An EPA assessment of
these responses reported borderline statistical increases in hepatic
neoplastic nodules and carcinomas (combined) in rats and mice following
ingestion of DCM in drinking water for 2 years. Liver and lung neoplasms
in mice and benign neoplasms in the mammary gland in rats were reported
following inhalation exposure to DCM for 2 years. In one study, sarcomas
were observed in the salivary gland region in male rats following
-------
32 Section 4
inhalation of DCM for 2 years; however, these tumors have not been
repeated in other bioassays on rats. Epidemiological studies found no
association between DCM exposure and liver and lung tumors in humans.
Based on the weight of evidence from animal studies, DCM was
classified by EPA as a probable human carcinogen; however, metabolic
data pointing to species differences in the utilization of the DCM
metabolic pathways indicate that risks to humans are lower than those
determined for laboratory animals.
4.2 TOXICOKINETICS
4.2.1 Overview
Methylene chloride is a small lipophilic molecule that is rapidly
absorbed from the alveoli of the lung into the systemic circulation. It
is also readily absorbed from the gastrointestinal (GI) tract. Following
GI tract absorption, DCM may be subject to first-pass hepatic metabolism
and elimination before reaching the systemic circulation. Dermal
exposure to DCM also results in absorption but at a slower rate than
other exposure routes. Absorption and distribution of DCM can be
affected by a number of factors, including dose level, dose vehicle,
physical activity, duration of exposure, and amount of body fat.
Methylene chloride is metabolized in vivo via two pathways: (1) an
oxidative (MFC) pathway mediated by the P-4SO system that yields CO and
C02 and (2) a glutathione-dependent (GST) pathway that only yields C02-
The MFO pathway is saturable at air concentrations of a few hundred
parts per million. However, the GST pathway shows no indication of
saturation at inhaled concentrations of up to 10,000 ppm. In vitro
studies have also demonstrated two metabolic pathways. An oxidative
pathway mediated by the P-450 system yields CO, and a second pathway
mediated by a glutathione-dependent reaction yields formaldehyde and
formic acid, which are further metabolized to C02.
Elimination of DCM from the body is primarily via expired air from
the lungs as unchanged parent compound or as CO and C02, the major
metabolites. The dose is a major determinant of the elimination product.
At low doses of DCM, a large percentage of the administered dose is
metabolized to CO and C02. However, the percentage of administered dose
that is metabolized is reduced as the dose of DCM is increased. In this
case, more of the unchanged parent compound is exhaled in expired air. A
small fraction of absorbed DCM has been detected in urine and feces.
The results of recent pharmacokinetic studies suggest that the
parent compound and/or reactive metabolites produced by the GST pathway
are the source of DCM-induced carcinogenicity. Based on these studies,
it has been postulated that the activity of the GST pathway in humans Ls
less than that of mice and might only become significant when the P-450
pathway has been saturated. Because of its low chemical reactivity, DCM
itself is unlikely to be directly Involved in carcinogenesis.
Consequently, metabolism of DCM by GST appears to be important in
carcinogenesis. Recent studies indicate that the GST pathway is less
active in rats, hamsters, and humans than in mice.
-------
ToxicologLcal Daca 33
4.2.2 Absorpt ion
4.2.2.1 Inhalation
Human. The principal route of human exposure to DCM is inhalation.
Absorption is rapid, followed by a plateau of blood concentration in
several hours. At low levels of exposure, blood concentrations of DCM
increase linearly with exposure level. However, at high concentration
levels, saturation occurs. Riley et al. (1966) reported that in one test
subject exposed to 100 ppm DCM for 2 h, the amount of DCM absorbed was
initially 70%, but gradually decreased to 31% of the DCM content of
inspired air. Similarly, 70 to 75% of inhaled vapor of DCM was absorbed
in human subjects exposed by inhalation to 50, 100, 150, or 200 ppm
(174. 347, 521, or 694 mg/m3) DCM for 7.5 h on a single occasion
(DiVincenzo and Kaplan 1981). The resulting pulmonary uptake was found
to be 5.54, 10.70, 15.38, and 21.07 mmol (471, 909, 1,306, and
1,790 mg), respectively. The percent absorption was relatively constant
over the range of exposures evaluated. McKenna et al. (1980) exposed
volunteers to 100 or 350 ppm (347 or 1,215 mg/m3) of DCM for 6 h. Their
data showed that the blood level of DCM for both concentrations reached
a steady state in -2 h.
The amount of DCM absorbed increased with duration of exposure and
physical activity (resulting in increased ventilation and cardiac
output). Physical activity for 0.5 h during exposure to 250 or 500 ppm
DCM doubled absorption but decreased retention from 55 to 40% because of
a threefold (6.9 to 22 L/min) increase in ventilation rate (Astrand et
al. 1975). Methylene chloride absorption was also related directly to
the degree of obesity in human subjects (Engstrom and Bjurstrom 1977).
Obese subjects absorbed 30% more DCM than lean subjects when exposed to
75 ppm for 1 h.
Animal. The magnitude of DCM uptake depends,on several factors,
including inspired air concentration, pulmonary ventilation, duration of
exposure, the rates of diffusion into blood and tissues, and solubility
in blood and the various tissues. The concentration of DCM in alveolar
air, in equilibrium with pulmonary venous blood content, asymptotically
approaches the concentration in the inspiratory air until a steady-state
condition is reached (EPA 1985a). After tissue and total body steady
state is reached during exposure, uptake is balanced by elimination
through the lungs and other routes, including metabolism.
DiVincenzo et al. (1972) investigated the absorption of DCM (99%
purity) in dogs (fasted male beagle, number of animals per dose not
specified) exposed by inhalation to 100, 200, 500, or 1,000 ppm (347,
694, 1,735, or 3,470 mg/m3) DCM for 2 or 4 h. Expired air and blood
concentrations of DCM were reportedly proportional to the magnitude of
exposure. Absorption of DCM was reportedly a function of its solubility
in blood and tissues, the cardiac output, and respiratory rate. No
quantitative data were presented to support the authors' conclusion.
MacEwen et al. (1972) determined blood DCM concentrations to be
directly proportional to exposure concentrations when dogs exposed for
16 days to 1.000 ppm (3,474 mg/m3) and 5,000 ppm (17.370 mg/m3)
exhibited blood DCM levels of 36 and 182 mg/L, respectively. Total
equilibrium can be assumed to have occurred in these animals (EPA
-------
34 Section 4
1985a). Similar values can be calculated from the data of Latham and
Potvin (1976). They found a proportional relationship in rats between
DCM blood and inspired air concentrations over a range of 1,000 to 8,000
ppm (3,474 to 27,792 mg/m3) during a 6-h exposure.
In contrast to these findings of a direct proportional relationship
between inspired air concentration of DCM and blood level in man and
other animals, McKenna et al. (1982) reported a greater than
proportionate increase of blood concentration with inhalation exposure
concentration in rats. Male Sprague-Dawley rats were exposed for 6 h to
50, 500, and 1,500 ppm DCM (173, 1,737 and 5,211 mg/m3). The data from
McKenna et al. (1982) indicate that the whole blood and plasma levels of
DCM increase disproportionately with an increase in inspired air concen-
tration. Furthermore, calculation of the blood/air ratio for these data
provide increasing values of 5.75, 5.97, and 7.59 for 50, 500, and 1,500
ppm, respectively. McKenna et al. (1982) suggest that the resultant
increase in blood DCM concentration is greater than that predicted by
increments in the inspired air because of a rate-limited metabolism of
DCM in the rat. Thus, at low inspired air concentrations (below
saturation of metabolism), the blood/air ratio is less (because of rapid
metabolism) than that at high inspired air concentrations (above
saturation of metabolism). At the highest dose level, the blood/air
coefficient is in agreement with values reported by other investigators.
4.2.2.2 Oral
Human. No studies were found in the available literature on the
oral absorption of DCM in humans.
Animal. Limited direct absorption studies in rats and mice
demonstrated that DCM was readily absorbed from the gastrointestinal
tract.
Methylene chloride levels detected in gut segments up to 40 min
posttreatment were similar between doses in rats administered single
oral doses of nonradioactive DCM (in water) at 50 or 200 mgAg (Angelo
et al. 1986a). Sixty percent of the administered dose (200 mgAg) was
recovered from the upper gastrointestinal tract <10 min posttreatment
(20% recovery after 40 min). The amount of DCM in the lower
gastrointestinal tract accounted for <2% of the administered dose up to
the 40-min test interval.
In mice administered oral doses of nonradioactive DCM at 10 or 50
msAg (in water), -25% of the administered dose was detected in the
upper gastrointestinal tract within <20 min (Angelo et al. 1986b).
Similarly, after treatments with DCM at 10, 50, or 1,000 mg (in corn
oil), -55% of the administered dose was detected in the upper gut
segment and remained there 2 h (Angelo et al. 1986b).
Reported findings that DCM is metabolized to CO and C02 and that
unchanged DCM is eliminated in the breath are in support of findings
from limited direct absorption studies demonstrating the absorption of
DCM when ingested. A single oral dose of 1 or 50 mgAg ^C-DCM
administered to rats was eliminated in the breath as unchanged DCM (12 3
or 72.1%, respectively) and as metabolites (primarily CO and O>2 at 88
and 28%, respectively) within 48 h (McKenna and Zempel 1981). Mice
-------
lexicological Data 35
excreted 40% of the administered dose (100 mg/kg) in expired air as
unchanged DCM and 45% as metabolites CO and C02 within 96 h (Yesair et
al. 1977).
4.2.2.3 Dermal
Human. No studies were found in the available literature on the
dermal absorption of DCM in humans.
Animal. Data show that DCM can be absorbed through the skin of
laboratory animals. Maksimov et al. 1977 (cited in NIOSH 1976) immersed
two-thirds of the tail of 128 white rats and measured the DCM
concentration in various tissues (lung, liver, brain, kidney., heart, and
fat) by gas chromatography after 1-, 2-, 3-, and 4-h exposures. Small
increases were seen in most tissues after 1 or 2 h of exposure, and DCM
concentrations in fatty tissues increased markedly after 3 h of
exposure. After 4 h of exposure, DCM concentrations remained elevated in
fatty tissues and were increased in all other tissues studied.
4.2.3 Distribution
4.2.3.1 Inhalation
Human. There is some evidence for accumulation of DCM in body fat.
However, it appears to reach steady state and wash out rapidly. Engstrom
and Bjurstrom (1977) exposed 12 male subjects (6 slim and 6 obese) to
750 ppm of DCM (2,600 mg/m3) for 1 h. The total uptake of DCM was 1,116
± 34 mg by the slim group and 1,445 ± 110 mg by the obese group. On a
milligram-per-kilogram basis, the uptake was IS.6 mg/kg for the slim
group and 15.0 mg/kg for the obese group. Needle biopsies showed that
the adipose tissue contained -8 to 35% of the average total uptake for
both groups. The amount of DCM absorbed correlated highly with the
degree of obesity and body weight. In the six slim subjects, the
concentration in the adipose tissue during the 4-h period after exposure
was approximately twice that of the six obese subjects. However, despite
lower concentrations, the obese subjects had a greater calculated amount
of DCM in the total fat depots of the body.
McKenna et al. (1980) exposed volunteers to 100 or 350 ppm of DCM
for 6 h and measured blood and exhaled air levels of DCM, CO-Hb, and
exhaled CO. At the end of the 6-h exposure, the CO-Hb concentration of
the group exposed to 350 ppm of DCM was 1.4-fold higher than that of the
group exposed to the lower dose. Likewise, the concentration of exhaled
CO in the high-dose group was 2.1-fold higher than that of the group
exposed* to 100 ppm. McKenna et al. (1980) concluded that their finding
of a nonllnearity between administered dose and the CO-Hb and CO levels
is an indication that metabolic saturation was approached.
Animal. In rats exposed to 14C-DCM at 500 ppm (1,735 mg/m3) for
1 h, radioactivity was detected in the liver, brain, and fatty tissue.
Concentrations fell by 25, 75, and 90%, respectively, at 2 h following a
1-h compound exposure (Carlson and Hultengren 1975).
Following the exposure of rats to air containing 200 ppm DCM for
6 h/day for 5 days, tissue concentrations were measured in the brain,
blood, liver, and perirenal fat on the fifth day of exposure after
-------
36 Section 4
0 (18-h exposure on day 4), 2, 3. 4, and 6 h of exposure (Savolainen et
al. 1977). Although no absorption factors were discussed, the
persistence in perirenal fat before exposure on the fifth day indicated
considerable retention in fat relative to other tissues.
4.2.3.2 Oral
Human. No distribution studies were found in the available
literature on the oral administration of DCM in humans.
Animal. In tissue distribution studies in which male Sprague-
Dawley rats were administered single oral (gavage) doses of DCM (14C-DCM
at 1 or 50 mg/kg), the highest concentration of radioactivity was
detected in the liver, kidney, and lung and the lowest in fat. Tissue
14C activity represented primarily metabolites (McKenna and Zempel
1981).
Methylene chloride administered orally to rats in single doses of
50 or 200 mg/kg over a period of 14 days was detected in the blood.
liver, and carcass (Angelo et al. 1986a). The average levels of DCM
decreased rapidly in the blood and liver between 10 and 240 min, but the
maximum carcass concentration occurred at the intermediate 30-min time
point. Methylene chloride concentrations in blood were generally less
than proportional to dose, whereas liver and carcass concentrations were
approximately proportional to dose. In studies with mice, DCM was
administered by gavage in a water vehicle at 50 mg/kg for 14 days
(Angelo et al. 1984b). Four hours following dosing, all of the DCM
concentrations in the blood and in most tissue samples were below the
limit of detection. Between days 1 and 14, the DCM concentration in the
10-min blood samples tended to decrease, whereas the levels at the same
time point increased for the liver and remaining carcass. Following a
500- and 1,000-mg/kg treatment in corn oil, the rate of decline of DCM
in the blood was slower than was observed for the treatment in water
Blood concentrations between treatments, which were approximately
proportional to dose when compared at the same time points as DCM
concentrations in the liver and carcass, also decreased more slowly
following administration in corn oil rather than in water. However,
there was no consistent pattern in the elimination profiles for a given
dose treatment when tissue concentrations at similar time points were
compared between days during the course of the 14-day dosing schedule,
especially for the liver.
4.2.3.3 Dermal
Human. No distribution studies were found in the available
literature on the dermal administration of DCM in humans.
Animal. No distribution studies were found in the available
literature on the dermal administration of DCM in animals.
4.2.4 Metabolism
4.2.4.1 Inhalation
Human. Several groups of investigators have studied the formation
of CO and CO-Hb in human subjects exposed to DCM. Carboxyhemoglobin
-------
Toxicological Daca 37
concentrations (calculated from measurements of CO in exhaled air) were
measured in four male plastic film workers (20 to 33 years old, two
nonsmokers, two smokers agreed to abstain) exposed to 180 to 200 ppm
(625 to 694 mg/m3) of DCM for 8 h (Ratney et al 1974). The CO-Hb
concentration, expressed as percent saturation of hemoglobin with CO,
was about 4.5% saturation at the beginning of the workday and rose to
about 9% saturation after 8 h of exposure. The 24-h time-weighted CO-Hb
concentration was 7.3% saturation.
Astrand et al. (1975) exposed 14 human subjects (males 19 to 29
years old) to DCM by inhalation and measured arterial CO-Hb
concentrations during exposure and for up to 2 h after the end of the
exposure. The concentration of CO-Hb increased both during and after
exposure. The authors reported that a concentration of about 5.5%
saturation was reached with an exposure to 500 ppm (1,750 mg/m3).
The observations by Stewart et al. (1972) that human subjects (11
males, aged 23 to 43 years, nonsmokers) exposed by inhalation to 500 to
1,000 ppm (1,735 to 3,470 mg/m3) DCM (99.5% pure) for 1 or 2 h
experienced elevated CO-Hb concentrations suggested that DCM was
metabolized to CO. The CO-Hb concentrations rose to an average of 10 1%
saturation 1 h after the exposure of three subjects to 986 ppm (3,421
rag/m3) DCM for 2 h. The mean CO-Hb concentration (3.9% saturation at
17 h postexposure) remained elevated above the preexposure baseline
value (1 to 1.5% saturation). The exposure of eight subjects to 515 ppm
(1,787 mg/m3) DCM for 1 h increased the CO-Hb level, which also remained
elevated above baseline for more than 21 h.
Peterson (1978) exposed human subjects (11 males aged 20 to 39
years and 9 females aged 20 to 41 years) by inhalation to 50, 100, 250,
or 500 ppm (174, 347, 868, or 1,735 mg/m3, chemical purity not
specified) DCM for 1, 3, or 7.5 h for up to 5 successive days per week
for 5 weeks. It was found that (1) CO-Hb concentrations could be
predicted from DCM exposure parameters (but the breath concentrations of
DCM correlated better with exposure parameters that did CO-Hb
concentrations), (2) no differences in DCM metabolism between male and
female subjects were detectable, and (3) no acceleration of DCM
metabolism to CO occurred during exposure for 5 weeks to concentrations
ranging from 100 to 500 ppm (347 or 1,735 mg/m3) DCM.
Elevated urinary formic acid contents have been reported in film
workers exposed by inhalation to DCM, indicating that DCM is metabolized
to formic acid by humans (Kuzelova and Vlasak 1966, cited in NIOSH
1976). Formic acid was present in urine samples from most (number not
specified) of the 33 film workers exposed for an average of 2 years to
contaminated air. The authors reported that concentrations in the
workplace air systematically exceeded 0.5 mg/L (500 mg/m3) DCM and
occasionally exceeded 1.75 mg/L (17,500 mg/m-*).
Animals. Fodor et al. (1973) observed that albino rats (number of
animals and sex not stated) exposed by inhalation to 0, 50, 100, 500, or
1,000 ppm (0, 174, 347, 1,735, or 3.470 mg/m3) DCM (purity not
specified) for 3 h showed CO-Hb formation (0.4, 3.2, 6.2, 10.5, or 12 5%
saturation, respectively), confirming the observation that DCM is
metabolized to CO. Similarly, Carlson and Hultengren (1975) reported
that Sprague-Dawley rats (ten male) exposed by inhalation to ^C
-------
38 Section 4
(1,935 mg/m3 for 1 h) produced l^C-CO, and the amount of radioactivity
Ln CO extracted from the blood was highly correlated to the amount of
CO-Hb formed in the blood.
Male New Zealand rabbits (number not specified) exposed via
inhalation to 5,000 to 10,000 ppm (17,350 to 35,700 mg/m3) DCM for 20
min showed elevated CO-Hb concentrations (Roth et al. 1975). The authors
did not present specific values for the percent CO-Hb produced at each
exposure; however, they did show results to demonstrate that increases
in CO-Hb concentrations were both dose-dependent and time-dependent.
CO-Hb concentrations reached a maximum in 2 to 3 h and returned to
control values by 8 h. A linear dose-response relationship between
inhalation of increasing concentrations of DCM and increasing CO-Hb was
also observed when four rabbits were exposed to 1,270 to 11,520 ppm DCM
(4,407 to 39,974 mg/m3, purity not specified) for a 4-week period (days
per week and hours per day not specified). However, the authors reported
that rabbits exposed to similar DCM concentrations had changes in CO-Hb
levels that varied by up to a factor of 2.
McKenna et al. (1982) reported that DCM is metabolized to CO and
C02. In rats, inhalation of 50 ppm for 6 h resulted in 26 and 27% of the
body burden being recovered as expired CO and C02, respectively, during
the first 48 h after the end of the 6-h inhalation period. At 1,500 ppm,
these numbers were 14 and 10%, respectively. A lesser percentage of the
initial dose is metabolized to these end points at the high dose.
Gargas et al. (1986) studied the in vivo metabolism of inhaled DCM
in male Fischer 344 rats. They demonstrated that DCM displays complex
uptake behavior, with both first-order and saturable components of
metabolism. Gargas et al. (1986) compared plasma concentrations of CO-Hb
in rats pretreated with pyrazole (which inhibits P-450 oxidation) or
2,3-epoxypropanol (2,3-EP) (which depletes glutathione) to assess the
relative contribution of each pathway to the total metabolism of DCM.
Pretreatment with pyrazole essentially abolished CO production by the
high-affinity saturable P-450 pathway. Concentrations of CO-Hb following
2,3-EP pretreatment were increased 20 to 30% compared with untreated
controls. Gargas et al. (1986) concluded that the effect of pyrazole
pretreatment provides support for the involvement of cytochrome P-450 in
the oxidation of DCM to CO.
The in vivo pharmacokinetics of DCM and its major metabolites, CO
and C02, were determined in F344 rats and B6C3F1 mice both during and
immediately after a 6-h inhalational exposure to 500, 1,000, 2,000, and
4,000 ppm DCM (CEFIC 1986b). An assessment has been made of the relative
utilization by the two species of the two known pathways of DCM
metabolism. Maximum blood levels of DCM were reached within 3 h of the
start of exposure and maintained at a constant level until the end of
exposure when they declined rapidly in both species. The cytochrome
P-450 pathway leading to CO and CO-Hb was shown to be saturated at the
500-ppm exposure level. After saturation of this pathway had occurred,
the blood levels of DCM in the rat increased almost linearly with dose,
indicating little further metabolism in this species. In contrast, there
was evidence for significant metabolism of DCM in the mouse at high dose
levels by the glutathione pathway, which leads to C02. Comparison of
expired C02 levels after 4,000-ppa exposure for 6 h showed almost an
-------
Toxicologies! Data 39
order of magnitude more C02 produced per kilogram of body weight in the
mouse than in the rat. A marked difference was seen in the rate of
clearance of DCM from tissues, as measured by its elimination in expired
air. Although cleared from blood rapidly in both species, the rate of
clearance from rat tissues was markedly slower than in the mouse. This
slow release in the rat sustained metabolism for up to 8 h after the end
of exposure and, consequently, had a marked effect on the overall body
burden of metabolites. DCM was cleared from tissues in the mouse in less
than 2 h. Overall, saturation of the cytochrome P-450 pathway occurred
at similar levels in both species, but significantly more DCM was
metabolized by the glutathione pathway in the mouse when assessed either
from the blood levels of DCM or by C02 formation at high dose levels.
Two physiologically based pharmacokinetic models have been
formulated to predict the disposition of DCM and its metabolites. A
model developed by Andersen et al. (1987) is based on inhalation
exposures, whereas an alternative model developed by Angelo and
Pritchard (1984) is based on intravenous and oral exposures. The latter
model is discussed in detail in Sect. 4.2.3.2. Physiologically based
pharmacokinetic models differ from conventional compartmental models in
that they are based to a large extent on the actual physiology of the
species under investigation (Clewell and Andersen 1985). Instead of
using compartments based on experimentally derived time-course data,
physiologically based models utilize compartments that accurately
represent organ and tissue volumes, blood flow rates, and tissue
partition coefficients. A model derived from this approach can
qualitatively predict the time course of xenoblotic metabolism without
being based directly on experimentally derived time-course data. The
result is a model that predicts quantitative interspecies differences in
xenobiotic absorption, distribution, metabolism, and elimination. Such
models can be used to describe intraspecies and interspecies differences
resulting from compound administration by different routes of exposure.
Eventually, as the model is further refined by incorporating additional
compartments and processes and by further iterating parameters, it
becomes possible to perform quantitative extrapolations well outside the
doses used in experimental studies.
Ramsey, and Andersen (1984) developed a physiological
pharmacokinetic model for examining the kinetic behavior of inhaled
vapors and gases that are essentially nonirritating to the respiratory
tract. Andersen et al. (1987) modified this model to study the metabolic
disposition of DCM. The model consists of a series of simultaneous
mass-balance differential equations that quantify the rate of change of
the DCM concentration within tissues of the body over a specified period
of time. The tissues are grouped into five compartments representing the
lung, fat, liver, richly perfused organs, and slowly perfused organs.
This model differs from the model described by Ramsey and Andersen
(1984) because of the addition of a distinct, metabolically active lung
compartment that is located between a gas exchange compartment and the
systemic arterial blood. The model assumes that the inhaled air in the
lung and pulmonary blood quickly achieves and maintains steady-state
conditions throughout the course of exposure. None of the other organs
are assumed to be in steady state. In this model, DCM enters the body
through inhalation, with absorption into the pulmonary blood via gas
-------
40 Seccion 4
exchange in the lung compartment. Metabolism then occurs by two pathways
in both the lung and liver compartments. The MFO pathway, which is
saturable, is described by a Michaelis-Menten type equation. Metabolism
by the GST pathway, which has not been demonstrated to be saturable
(Gargas et al. 1986), is described as a linear, first-order process.
Andersen et al. (1987) used the pharmacokinetic model to provide
quantitative descriptions of the rates of metabolism by the two pathways
and the levels of DCM in various organs of four mammaliam species (rats,
mice, hamsters, and humans). The model, which incorporates a variety of
variables representing the blood and tissue concentrations of DCM,
exhaled DCM, and instantaneous rates of metabolism by each pathway, was
validated by comparing predictions of DCM blood concentration and time-
course data with experimentally derived results obtained with F344 racs,
Syrian Golden hamsters and B6C3F1 mice, and human volunteers. The
predicted values for each of the four species were in agreement with the
experimental data. The model was also shown to predict reasonably well
the appearance and elimination of DCM metabolites.
Using this model, Andersen et al. (1987) estimated target tissue
doses of DCM and its metabolites in the two bioassays conducted with the
B6C3F1 mouse. In the inhalation study conducted by NTP (1986).
significant increases in lung and liver tumors had been observed. In
contrast, the drinking water study had failed to show a dose-related
increase in the incidence of either type of tumor in the same strain of
mouse. Six different dose surrogates were estimated for the B6C3F1 mouse
under the conditions of each study:
• Area under the liver concentration/time curve
• Area under the lung concentration/time curve
• Virtual concentration of metabolites derived from the MFO pathway
in liver
• Virtual concentration of metabolites derived from the MFO pathway
in lung
• Virtual concentration of metabolites derived from the GST pathway
in liver
• Virtual concentration of metabolites derived from the GST pathway
in lung
The lasc four dose surrogates represent the expected tissue
exposures of several reactive metabolites that are too short-lived to
measure directly (Andersen et al. 1987). They are based on the
assumption that the tissue dose of a toxic metabolite is proportional to
the integral of the rate of formation of the metabolite divided by
tissue volume. Table 4.1 summarizes the dose surrogates estimated by
Andersen et al. (1987) for the chronic bioassays performed by NTP (1986)
and Serota et al. (1984). Dose surrogates related to the MFO pathway
were nearly identical in the two studies. However, significant
differences were observed in the dose surrogates related to the activity
of the GST pathway in the inhalation and oral studies.
Tumor incidence in B6C3FI mice observed in the NTP (1986) bioassay
correlated with the tissue area under the concentration curve (AUC) and
-------
Toxicological Daca
Table 4.1. Comparison of average daily values of dose surrogates
in lung and liver tissue of female B6C3F( mice in
two chronic bioassays"
Parameter
Dose surrogate related to
MFO activity in the liver
Dose surrogate related to
GST activity in the liver
Dose surrogate related to
the concentration of DCM
in the liver
Dose surrogate related to
MFO activity in the lung
Dose surrogate related to
GST activity in the lung
Dose surrogate related to
the concentration of DCM
in the lung
Inhalation
2,000
3,575.0*
851.0*
362.0*
1,531.0*
123.0*
381.0"
(ppm)
4,000
3,701.0
1,811.0
771.0
1,583.0
256.0
794.0
Drinking water
(250 mg/kg/day)
5,197.0
15.1
6.4
1,227.0
1.0
3.1
"The chronic bioassays were performed by NTP 1986 and Serota
et al. 1984.
*Units are milligrams of DCM metabolized per liter of tissue.
'Units are (rag/liter)-h.
Source: Adapted from Andersen et al. 1987.
-------
42 Seccion 4
che amount of DCM metabolized by the GST pathway. A similar correlation
was not observed with the MFO pathway. The MFO pathway is saturable, but
the GST pathway is not saturable at dose levels up to 10,000 ppm of DCM.
The levels of GST-mediated metabolites increase disproportionately at
high concentrations of DCM.
The model predicts that in the NTP (1986) study, the values of the
liver dose surrogate related to GST activity are 851 and 1,811 mg/L per
24 h after a 6-h exposure to 2,000 and 4,000 ppm of DCM, respectively.
In contrast, from the drinking water study (Serota et al. 1984), the
liver dose surrogate was predicted to be only 15.1 mg/L per 24 h at a
dose level of 250 mgAg/day. Similarly, the values of the lung dose
surrogate are 123 and 256 mg/L per 24 h after 2,000 and 4,000 ppm,
respectively, whereas in the drinking water study, the dose surrogate is
only 1.0 mg/L per 24 h at a dose level of 250 mgAg/day. Significant
differences were also observed in the dose surrogates related to
concentrations of DCM in the target tissues. The model predicted that in
the NTP bioassay, the dose surrogate values related to the concentration
of DCM in the liver were 362 and 771 (mg-h)/L after 2,000 and 4,000 ppm,
respectively, and the values for the dose surrogate related to DCM in
the lung were 381 and 794 (mg-h)/L. In contrast, the values for these
parameters were 6.4 and 3.1 (mg-h)/L at a dose level of 250 mgAg/day in
the drinking water study. These findings suggest that the tumor
incidences observed in the two studies are not due to reactive
intermediates from the MFO pathway. The estimated levels of these
metabolites were similar in cases where tumors appeared and in others
where they did not appear. The results are consistent with the
hypothesis that (1) tumorigenicity is related to the production of
reactive intermediates by the GST pathway, or (2) tumorigenicity is
related to the presence of DCM in the target organs.
4.2.4.2 Oral
Human. No metabolism studies data were found in the available
literature on the oral administration of DCM in humans.
Animal. Angelo and Pritchard (1984) developed a physiologically
based pharmacokinetic model describing the disposition of DCM following
exposure by intravenous dosing and by gavage. This model differs from
the model of Andersen et al. (1987) in that it divides most of the
organs into two subcompartments, a flow-limited vascular region and a
membrane diffusion-limited extravascular region. The model includes
compartments for venous and arterial blood pools, major organs (liver,
kidney, lung), the GI tract, and the carcass tissue representing a large
fraction of the distribution volume of DCM in the body. Simulation
studies conducted by Angelo and Pritchard (1984) on dose-vehicle effects
on metabolism indicate that corn oil used as the vehicle for
administering DCM can affect both the uptake and distribution of DCM to
target tissues and can also affect metabolism.
In subsequent studies with the B6C3F1 mouse (Angelo et al. 1986a)
and with the F344 rat (Angelo et al. 1986b), it was found that the route
of exposure and the composition of the dosing solution had a significant
effect on the pharmacokinetics of DCM. The metabolism of DCM by mice
given single intravenous doses of 10 or 50 mg of 14C-DCM was
-------
Toxicologies! Data 43
characterized by dose-dependent biotransformatlon to C02 and CO and
rapid pulmonary clearance of the unchanged parent compound. Elimination
rate constants were estimated to be 0.156/min (half-life - 4.43 min) for
the 10-mg dose and 0.116/min (half-life - 5.98 min) for the 50 mg-dose.
These parameters were significantly different (P < 0.05), indicating
dose-dependent elimination. When DCM was administered orally to mice in
single gavage doses for 14 days at levels of 50 mg/kg/day in water and
500 or 1,000 mg/kg/day in corn oil, rapid absorption and elimination
were observed in the water vehicle group, whereas distinctly slower
trends were observed in the corn oil vehicle group (Angelo et al.
1986a).
The route and level of exposure were also found to have a
significant effect on the disposition of DCM in the rat (Angelo et al.
1986b). Using the two-compartment model, Angelo et al. (1986a) estimated
that the beta elimination rate constants were 0.058/min (half-life -
11.9 min) in rats receiving a single intravenous dose of 10 mg and
0.028/min (half-life - 23.5 min) in rats administered a single 50-mg
intravenous dose of DCM. The disposition rate constants were
significantly different (P < 0.05), indicating dose-dependent
elimination from the blood. The metabolism of DCM was also found to be
dose dependent. When DCM was administered to rats by gavage at daily
doses of 50 or 200 mg/kg/day for 14 days, rapid absorption and
distribution to the tissues were observed. Dose-dependent
biotransformation of DCM to C02 and CO and rapid pulmonary clearance of
the unchanged parent compound characterized the disposition of DCM.
McKenna and Zempel (1981) reported that in rats (250 g) given 1 or
50 mg/kg of l^C-DCM, -5% or 2% of the dose, respectively, was excreted
in the urine within 48 h.
Mice given DCM orally in corn oil at a dose of 100 mg/kg eliminated
40% of the dose in the expired air as unchanged DCM, 20% as CO, and 25%
as C02 within 96 h; a dose of 1 mg/kg DCM was metabolized to CO (45%)
and C02 (50%) (Yesiar et al. 1977).
4.2.4.3 Dermal
Human: No metabolism studies were found in the available
literature on the dermal administration of DCM.
Animal. McDougal et al. (1986) developed a physiological model for
the penetration of organic vapors through skin in vivo. The model can be
used to protect blood concentrations (after dermal vapor exposures in
the rat) when chemical distribution coefficients, physiological and
metabolic parameters, and skin permeability constants are known.
Permeability constants for DCM were calculated by using a
physiologically based pharmacokinetic model for dihalomethanes (Gargas
et al. 1986) to relate blood concentrations during dermal vapor
exposures to the total amount of chemical that was absorbed through the
skin. A skin compartment was added to the model which had input based on
the permeability-area concentration product. This predictive model
adequately described blood concentrations after DCM dermal vapor
exposures over a wide range of doses.
-------
44 Section 4
4.2.4.4 In vitro studies
In vitro studies (Anders et al. 1977, Gargas et al. 1986)
demonstrated that the metabolism of DCM involved two pathways (Fig. 4 1)
Gargas et al. (1986), cited in EPA 1987a. predicted that the microsomal
metabolism of DCM might yield both CO and C02- The mechanism prediccs
that following the initial oxidation of DCM to formyl chloride, this
intermediate combines with glutathione and is then further metabolized
by a GST to C02. Gargas et al. (1986), cited in EPA 1987a, further
suggested that the formation of the formyl glutathione intermediate is
possible, assuming that formyl chloride is a relatively stable
intermediate.
The metabolism of DCM was compared in vitro using rat, mouse, and
hamster lung and liver fractions (CEFIC 1986a). Comparisons were also
made between metabolism in animal tissues and that in human liver in
vitro. Tissue homogenates were separated into microsomal and cytosolic
fractions to investigate the cytochrome P-450 and glutathione-S-
transferase dependent pathways of DCM metabolism, respectively. The
cytochrome P-450 pathway was assessed by measuring the conversion of DCM
to CO, and the glutathione-S-transferase pathway was determined by
measuring formaldehyde formation. Metabolic rates were determined ac a
series of substrate concentrations, and, where possible, the metabolic
rate constants Km and Vmax were obtained.
The most active tissue for metabolizing DCM by the cytochrome
P-450 pathway was the hamster liver, with a similar rate observed in
mouse liver. The rates for rat and human liver were similar but
significantly lower than those found in the mouse and hamster. A
parallel difference in response was seen in lung tissue, with rat lung
showing significantly lower metabolic rates than the mouse and hamscer
lung. Human lung tissue was not available.
For the glutathione-S-transferase mediated pathway, mouse liver was
considerably more active than any other tissue, the maximal rate being
more than 12-fold greater than the next most active tissue, the rat
liver. No activity could be detected for this pathway in either hamster
or human liver, even though these tissues were active with another
substrate for the glutathione-S-transferases. A low rate of metabolism
of DCM by this pathway could be detected in mouse lung but not in rat or
hamster lung. Metabolism by the glutathione pathway correlates well wich
the known carcinogenicity of DCM in animals, whereas metabolism by the
cytochrome P-450 pathway does not.
4.2.5 Excretion
4.2.5.1 Inhalation
Human. The urinary excretion of DCM was measured in 11 human
subjects after inhalation exposure (DiVincenzo et al. 1972). Less than
2% was detected in urine unchanged. In four subjects exposed to 100 ppm
(347 mg/m3) DCM (purity not specified) for 2 h, an average of 22.6 ng
DCM was excreted in the urine within 24 h after the exposure; in seven
-------
CYT P-450
CYTOSOL
Oj> s\ iA
NADPH i
GSH X
JH2-X
),<-
II
H'-
i
^X
<-—
>—
- NUCLEOPHILE?
(i.e.. GSH)
b ^H*
GS-CH2 -OH
CH20 + GSH
NAD*
-V°
I XH
C02
HCOOH * GSH
I
I
C02
H
GS-C
H
GSH
i
CO2
n
o
o
B)
n
Di
Fig. 4.1. Proposed pathways for melhylenc chloride metabolism.
-------
46 Section 4
subjects exposed to 200 ppm (694 mg/m3) DCM for 2 h, the corresponding
value was 85.5 /ig. No data were found on amounts recovered In feces or
urine.
Animals. No excretion studies were found in the available
literature on the inhalation exposure of DCM in humans.
4.2.5.2 Oral
Human. No excretion studies were found in the available literature
on the oral administration of DCM in humans.
Animal. In rats, a single oral dose, or 1 or 50 mg/kg 14C-DCM, was
eliminated in expired air as unchanged DCM (12.3 or 72%, respectively)
within 48 h. For corresponding duration and dose, fecal (<1%) and
urinary (5%, 2%, or the administered dose, respectively) eliminations
were low (McKenna and Zempel 1981).
4.2.5.3 Dermal
No excretion studies were found in the available literature on the
dermal administration of DCM in humans.
Animal. No excretion studies were found in the available
literature on the dermal administration of DCM in animals.
4.2.6 Discussion
The current evidence is not sufficient to identify with reasonable
certainty the carcinogenic mechanism of action of DCM. The available
data suggest that DCM produces a carcinogenic response via GST-mediated
metabolism. There is a strong correlation between GST activity and the
occurrence of tumors in mice. In addition, there is little evidence to
implicate either parent DCM or metabolites resulting from the
alternative MFO pathway.
The model developed by Andersen et al. (1987) provides a framework
for estimating the nonlinearity inherent in the metabolism of DCM by two
pathways used to different extents at high and low doses in the risk
estimation procedure. When applied to high-Co-low dose extrapolation,
the model is relatively Insensitive to major uncertainties in the
pharmacokinetic data. It accounts for the nonlinearities in the internal
doses across exposure levels that arise from dose-dependent changes in
absorption, distribution, excretion, and saturation of metabolism. It
characterizes the nonlinearity of metabolism via the GST pathway at low
and high doses as a result of saturation of the competing MFO pathway.
This model can be used to extrapolate to human DCM vapor exposure
conditions by substituting human physiological parameters for the animal
values. Andersen et al. (1987) used their model to estimate target tissue
doses of presumed toxic chemical species in humans exposed to DCM by
inhalation or by drinking water. Estimated target tissue doses in humans
exposed to low concentrations of DCM were several fold lower than linear
extrapolation from high-dose mice would predict. The EPA (1987a,b) has
pending an approximate ninefold reduction in its inhalation unit risk,
taking into account the model's results. Andersen et al. (1987) advocate
a much larger reduction, from 140 to 210 fold, based on a different
-------
lexicological Data 47
interpretation of EPA's surface area factor for interspecies extrapolation
Questions about interspecies extrapolation, using the model, result from
unresolved issues about the impact of differences in species sensitivity
to a given internal, target-tissue dose.
4. 3 TOXIC ITY
4.3.1 Overview
The toxic effects of DCM are varied. Methylene chloride may cause
acute lethality when animals are administered large doses orally,
intraperitoneally, subcutaneously, or by inhalation. Fatty degenerative
changes, glycogen depletion in the liver, and kidney damage were seen
after inhalation exposure to large doses of DCM. Methylene chloride was
toxic to the cardiovascular system at high doses. Decreased blood
pressure and increased heart rate were reported in primates. Central
nervous system effects included behavioral and performance deficits,
depression, anesthesia, coma, and death. Chronic oral exposure to DCM
via drinking water resulted in hepatic histopathological alterations,
decreased body weight gain, and biochemical changes in the blood of
rats. In animals, no prominent teratogenic potential has been shown to
exist for DCM. Results were negative in a two-generation reproduction
study. Mutagenic activity has been observed in some strains of bacteria
and yeast and in a mammalian cell culture line. Results were largely
negative in mammalian cells in vivo. Chronic exposure to DCM in drinking
water produced a significant increase in liver tumors in female rats
when compared with matched controls; however, the tumor incidences were
within historical control levels. No carcinogenic response was indicated
in mice. An EPA assessment of the results of these studies suggested a
borderline statistical increase in the incidence of hepatic neoplastic
nodules and carcinomas (combined) in female Fischer 344 rats and male
B6C3F1 mice. Sarcomas have been reported in the salivary gland region
of male rats; however, the authors suggested that a viral disease in
rats may have contributed to the tumorigenic response. The NTP reported
clear evidence of the carcinogenicity of DCM in female F344/N rats and
in B6C3F1 mice of both sexes in a chronic inhalation carcinogenicity
bioassay. Methylene chloride induced increased incidences of benign
neoplasms in the mammary gland in rats and of alveolar/bronchiolar
neoplasms and hepatocellular neoplasms in mice of both sexes.
4.3.2 Lethality and Decreased Longevity
4.3.2.1 Overview
Exposure to DCM can be fatal in humans and animals following
inhalation and ingestion. Lethal dose levels could not be determined in
humans; however, LCSO values of 11,000 to 16,000 ppm were reported. Oral
exposures were lethal at doses of 1,000 to 4,000 mg/kg.
4.3.2.2 Inhalation
Human. Case studies of DCM poisoning have demonstrated that
exposure can be fatal. One case of accidental death resulted from acute
DCM exposure during paint-stripping operations (Bonventre et al. 1977).
Methylene chloride concentration was not reported; however, it was
detected in various tissues, including the liver (14.4 mg/100 g of
-------
48 Section 4
tissue), blood (510 mg/L), and brain (24.8 mg/100 g of tissue). Another
death occurred following acute exposure to DCM being used as a paint
remover (Stewart and Hake 1976). In this case, no data were provided on
DCM concentrations or on the tissue levels of DCM detected.
No lethality data were found in the available literature following
chronic exposure to DCM.
Animal. When laboratory animals inhaled DCM, guinea pigs were more
susceptible than mice to its lethal effects (Table 4.2).
4.3.2.3 Oral
Human. No lethality studies were found in the available literature
on the oral administration of DCM in humans.
Animal. When exposed orally, CF-1 mice and Sprague-Dawley rats
were about equally susceptible to the lethal effects of DCM (Table 4.2).
4.3.2.4 Dermal
Human. No studies were found in the available literature on the
lethal effects of dermally applied DCM in humans.
Animal. No studies were found in the available literature on the
lethal effects of dermally applied DCM in animals.
4.3.2.5 Discussion
Two human case studies have demonstrated that DCM exposure can be
fatal. Methylene chloride was lethal when inhaled by animals at high
concentrations. LC50 values of 11,000 to 16,000 ppm were reported.
Similar responses were noted at 1,000 to 4,000 mg/kg following oral
administration. Based on animal studies, it appears that high levels are
necessary to cause mortality.
4.3.3 Systemic/Target Organ Toxicity
4.3.3.1 Overview
Various human and animal studies demonstrated that the liver and
the central nervous system (CNS) are the primary targets following DCM
exposure. The primary route of entry to the body for DCM is via
inhalation, and most of the studies found in the available literature
are concerned with inhalation. In acute experimental inhalation studies
in humans, DCM administered at concentrations in excess of 300 ppm for
up to 4 h altered behavioral performance, as manifested by decreased
visual and auditory functions. Similarly, various psychomotor tasks were
impaired, but these occurred at higher levels (800 ppm). Acute animal
studies support findings of DCM-induced effects in the central nervous
system. These effects occurred, however, at higher concentrations for
corresponding durations of exposure. Slight narcosis occurred in several
species at 4,000 to 6,000 ppm (2.5 to 6 h). Behavioral effects, as
manifested by the reduction in rapid eye movement during sleep, were
also demonstrated after 24 h (1,000 to 3,000 ppm).
-------
TOXLCOlogical Data
Table 4.2. Acute lethality of methylene chloride
Species
(strain/sex/No.)fl
Mouse (CF-l/M/50)
Mouse
(S.P.F, OF,/F/not
stated)
Mouse (Swiss/not
stated/80)
Guinea pig
( Hartley /M/60)
Mouse
(CF-l/M/65)
Rat
(Wistar/M/not
stated)
Rat
(Sprague-Dawley/
M/not stated)
Route
(duration)
Inhalation
(20 min)
Inhalation
(6h)
Inhalation
(8h)
Inhalation
(6h)
Oral
Oral
Oral
Effect Dose*
LC$o 26,710 ppm
(92,649 mg/m3)
LCso 14.155 ppm
(49,1 18 mg/m3)
LCso 16,189 ppm
(56, 176 mg/m3)
LCso 11, 600 ppm
(40,252 mg/m3)
LDjo 1,987 mg/kg
LD95 5.16mM/100g
(4.382 mg/kg)
LDso 1.6 mL/kg
(2,121 mg/kg)
References
Aviado et al.
1977
Gradiski et al.
1978
Svirbely et al.
1947
Balmer et al.
1976
Aviado et al.
1977
Ugazio et al.
1973
Kimura et al.
1971
"M = male, F •* female. No. =" total number of animals in lethality study.
* Expressed as exposure for inhalation route.
Source: Adapted from EPA 1985c.
-------
50 Section 4
Various inhalation and oral animal studies revealed mild liver
effects following DCM exposure. Alterations in liver cytochromes were
demonstrated in animal species following inhalation of 500 ppm DCM for
10 days. Cellular changes were observed at 100 ppm (100 days). In oral
studies, histomorphological alterations were reported in animals exposed
to 250 mg/kg/day OCM for 104 weeks.
Limited data show that high concentrations of DCM can cause upper
respiratory tract irritation and produce cardiovascular, ocular, and
renal effects.
4.3.3.2 Central nervous system
Central nervous system effects have been observed in humans in
experimental studies following DCM exposure. Alterations in behavioral
performance and various psychomotor tasks were evident after short-term
exposure. Neurobehavioral effects were reported in factory workers exposed
to DCM. Similarly, CNS effects have been demonstrated in animals following
acute exposure, but these occurred at exceedingly high dose levels.
Inhalation, human. A primary adverse health effect associated with
short-term exposure to DCM is impairment of CNS function (Table 4.3). In
experimental studies, inhalation of DCM for up to 5 h decreased visual
and auditory functions (>300 ppm) and various psychomotor tasks
(800 ppm) (Fodor and Winneke 1971, Winneke 1974). Similarly, CNS effects
were produced at higher dose levels and for short exposure periods as
alterations in visually evoked responses were detected 1 to 2 h
following exposure to 1,000 ppm (Stewart et al. 1972).
Longer-term exposure also produced CNS effects (Table 4.4).
Neurotoxicity was the most prominent symptom complex reported in over
100 cases involving occupational exposure to DCM. Welch (1987) reported
that workers from several industries, including auto parts production
and plastic and prosthesis manufacturing, presented a variety of CNS
complaints, including headaches, dizziness, nausea, memory loss,
parasthesia, tingling in hands and feet, and loss of consciousness.
These effects occurred during certain painting, cleaning, and spraying
operations:"Methylene chloride levels measured were up to 100 ppm, and
duration of exposure was 6 months to 2 years. Levels greater than 100
ppm (duration not specified) produced corresponding effects under
similar situations. It should be noted that workers were exposed
concomitantly to other unspecified solvents. Results of this study
should be viewed cautiously.
In another study, subjective assessments of sleepiness, physical
tiredness, and mental tiredness were evaluated in factory workers
(Cherry et al. 1983). A total of 56 workers were exposed to 28 to 173
ppm of DCM (in a 9:1 DCM/methanol atmosphere). The changes in parameters
measured were significantly greater (P < 0.05 for mental tiredness,
P < 0.01 for physical tiredness and sleepiness) only for the morning
shift, and the magnitude of the changes correlated in a statistically
significant manner with the blood CO-Hb levels at the end of the shift
Although no statistically significant changes were observed in two
objective tests (digit symbol substitution test and reaction time),
deterioration in performance on the morning shift correlated (P < 0.01)
with the end-of-shift blood concentration of DCM.
-------
Toxicological Data 51
Table 4.3. Short-term experimental metbylene chloride
inhalation exposures and reported effects in humans
Concentration
(ppm)
Duration
Effects
References
500-1,000 1-7.5 h/day CO-Hb percentages proportional
5 days/week to exposure concentration and
time; CNS depression at
1000 ppm
50-500 7.5 h Decreased dissociation of oxygen
5 days/week from Hgb in proportion to
exposure concentration
100 and 500 7.5 h/day Blood lactic acid increased
5 days/week slightly from exercise at 500 ppm,
not 100 ppm
317 and 751 4 h Depressed CFF," decreased
auditory vigilance performance
317, 470, 3-5 h Decreased performance of CFF,"
751 auditory vigilance, and
psychomotor tasks
"Critical Fucher Frequency.
Stewart et al. 1972
Forster et al. 1974,
cited in NIOSH 1976
Fodor and Winneke 1971
Winneke 1974
-------
52
Section 6
Table 4.4. Longer-term occupational methylene chloride
inhalation exposures and effects in humans
Concentration
(ppm)
Duration
Effects
References
Weiss 1967. cited in
NIOSH 1976
660-3,600 One worker. After 3 years: burning pain
several around heart, restlessness,
hours per day feeling of pressure,
for 5 years palpitations, forgetfulness,
insomnia, feeling of
drunkeness. After 5 years:
auditory and visual
hallucinations, slight
erythema of hands and
underarms. Diagnosed as
having toxic encephalosis.
28-173 Reversible subjective symptoms Cherry et al. 1983
-------
Toxicologies! Data 53
Inhalation, animal. Short-term inhalation studies showed that DCM
produced central nervous system effects (Table 4.5). In several species.
slight narcosis occurred at 6000 ppm after 2.5 h exposure (Ueinstein
et al. 1972); deep narcosis occurred in rats at 16,000 to 18,000 ppm
after 6 h exposure (Berger and Fodor 1968).
Behavioral effects have also been reported. A reduction in
paradoxical sleep was observed in rats exposed at 1,000 or 3,000 ppm for
24 h. This effect on sleep was not observed at 500 ppm (Fodor and
Uinneke 1971). Inhalation of 500 ppm for 6 h daily for 4 days resulted
in an increase in preening frequency in rats (Savoleinen et al. 1977).
In studies using the running-wheel technique, there was decreased
spontaneous motor activity in male rats exposed intermittently to 500
ppm DCM for 7 h/day, 5 days/week for up to 6 months (Heppel et al. 1944,
Heppel and Neal 1944).
An inhalation neurotoxicity study on DCM in rats exposed to 50,
200, and 2,000 ppm DCM for 90 days is currently under way. This study is
sponsored by Halogenated Solvents Industry Alliance (HSIA 1988) and
includes electrophysiology, a functional observational battery, and
neuropathology as end points. HSIA (1988) reported that preliminary
results show that DCM did not produce neurotoxic effects upon repeated
exposure in rats. Results of this study are expected to be available in
the spring of 1988.
Oral, human. No CNS or behavioral studies were found in the
available literature on the oral administration of DCM in humans.
Oral, animal. No CNS or behavioral studies were found in the
available literature on the oral administration of DCM in animals.
Dermal, human. No CNS behavioral studies were found in the
available literature on the dermal administration of DCM in humans.
Dermal, animal. No CNS or behavioral studies were found in the
available literature on the dermal administration of DCM in animals.
Discussion. Based on experimental data, it appears that impairment
of behavioral or sensory responses may occur in humans following acute
inhalation exposure to DCM at levels exceeding 300 ppm for short
duration, and the effects are transient. No data were found in the
available literature on CNS effects after oral or dermal exposure. The
CNS effects produced following exposure to DCM are probably due to DCM
alone or in combination with CO-Hb. Evidence has been provided which
shows that the MFO pr.thway (resulting in CO production) is mostly
saturable, producing maximum blood CO-Hb levels of <9%. These CO-Hb
levels are not sufficiently high enough to induce the CNS effects
observed following acute DCM exposure; therefore, it appears that
behavioral effects are probably due to DCM alone or in combination with
CO-Hb.
4.3.3.3 Hepatotoxicity
Available literature demonstrated that DCM can adversely affect the
liver in animals, and suggestive evidence for a similar effect in humans
was also found. In animal inhalation studies, cellular changes were
-------
54
Section
Table 4.3. Short-tern
exposures ud effects la
Concentration
(ppm)
14.500
Duration
2b
Effects
Mice — death
References
Flury and
Zermk 1931
10.000
4.000
6.000
15.000 and
20.000
40.000
2h
6h
6h
23.000-28.000
16.000-18.000
lib
6h
5.000-9.000
2.800
3.000 and 1.000
5,000
5.000
8h
14 h
24 b
30min/
day
7dayi
Mice — narcosis
Dogs — light narcosis after
2 5 h. rabbits after 6 h
Guinea pigs— slight narcosis
in 2 5 h. rabbits and cats
in 3-4 h, dogs in 2 h
Dogs — loss of pupillary and
corneal reflexes after
10-20 mm: complete muscular
relaxation after 25-35 mui;
reduction in blood pressure;
rapid narcosis at 20.000 ppm
Dogs — loss of pupillary and
corneal reflexes after
10-20 mm; complete muscular
relaxation after 16 min: 3 of
5 dogs died from progressive
hean failure due to cardiac
injury
Rats— electrical activity
stopped after 1.5 h
Rats— initial excitement
followed by deep narcosis,
decreased EMG tonus;
decreased EEC activity;
breathing difficulties:
tremor, electrical activity
stopped after 6 h
Long sleeping phase lacking
desynchronuation phase*
Rats— de
d proportion of
REM sleep to total sleep
Rats—suppressed REM sleep:
increased tune between two
REM periods; linear relation
between dose and response
Rats—decreased running
activity
Mice—initial increase in
physical activity followed by
decrease in food and water
intake, lethargy, increased
liver to body weight ratio
and liver fat. mild fatty
infiltrations, hydropic
degeneration of centnlobular
cells
Wemstem
et al. 1972
Von Oettingen
et al. 1949
Berger and Fodor
1968
Fodor and
Winneke 1971
Heppel and
Neal 1944
Weinstein
et al. 1972
-------
Tabfe4.5 (condoMd)
Toxicological Data 55
Concentration
(ppm)
Duration
Effects
References
5.200
500
5.000
4,500
1.2SO
6 h Fatty infiltration of liver Moms et al.
in guinea pigs. Effects were 1979
transient in mice
10 days Altered cytochromes P-450: Norpotb et al.
reduction in ammopynne 1974
/V-demethylase activity in
rats
10 days Elevation of enzyme activity Norpoth et al.
1974
10 days Increased maternal absolute Hardin and
and relative liver weight Maason 1980
and lowered fetal weight*
in rats
10 days Lowered fetal weights and Schwetz et al.
increased maternal average 197S
absolute liver weight in rats
Increased maternal liver
weights
Source. Adapted from NIOSH 1976. EPA 1985a. I985c.
-------
56 Section 4
demonstrated at 100 ppm (100 days), and liver cytochromes were altered
following a 10-day exposure at 500 ppm. It should be noted that hepatic
effects reported at 100 ppm were elicited upon continuous exposure without
recovery as opposed to the more traditional exposure protocol. An
increased incidence of hepatocellular vacuolization was observed in male
and female rats exposed to 500 ppm. Female rats exposed to 500 ppm DCM
also had an increased incidence of multinucleated hepatocytes (Nitschke
et al. 1982. 1988). In oral studies, histomorphological alterations were
observed in animals exposed to 50 mg/kg/day DCM for 104 weeks.
Inhalation, human. Welch (1987) reported a case of hepatitis in a
worker who was exposed to solvents. Methylene chloride was used in
combination with other unspecified solvents, but the DCM levels measured
in the serum were significantly higher than for the other solvents.
There were no exposure measurements reported for DCM or other solvents.
Several workers in similar work environments had abnormal liver function
tests, but no measurements of exposure were reported. Results from this
study should be viewed cautiously.
Inhalation, animal. Acute and chronic studies have revealed the
liver as a target organ following DCM exposure (Tables 4.5 and 4.6).
Acute studies showed that DCM altered liver structure and
cytochrome activity (Table 4.5). The inhalation of 5,200 ppm for 6 h
caused fatty infiltration in the liver of guinea pigs (Morris et al.
1979); transient fatty changes were also observed in mice exposed to
5,000 ppm for 7 days (Ueinstein et al. 1972). Following a 10-day
exposure to vapors of DCM, a significant increase in liver cytochrome
P-450 occurred in male SPF Wistar rats exposed to 500 ppm. The increase
did not occur in animals exposed to 5,000 ppm (Norpoth et al. 1974). No
statistically significant change occurred at the high dose. The author
reported that the inverse dose-response relationship for P-450 may be
due to the combined effect of DCM and CO. Differential enzymatic
induction was also reported. Reduced liver enzyme (aminopyrine N-
demethylase) activity occurred in animals exposed to 500 ppm; however,
activity was elevated in those animals exposed to 5,000 ppm (Norpoth et
al. 1974). After 28 days of exposure to DCM (250 ppm), no changes were
noted in liver enzymes (Veinstein et al. 1972).
Liver toxicity was also observed following longer-term exposures by
inhalation (Table 4.6). Continuous inhalation exposure to DCM (100 ppm)
for 10 weeks resulted in centrilobular fat accumulation in ICR mice. The
increase in fat was accompanied by a decrease in glycogen that persisted
with termination of the study at 10 weeks (Ueinstein and Diamond 1972.
cited in EPA 1985c). Cytoplasmic vacuolization and positive fat staining
were reported in mice exposed continuously via inhalation for 100 days
to 100 ppm DCM. Cytochrome P-450 was decreased but P-b5 was increased
(Haun et al. 1972). The Haun study also reported cytoplasmic vacuolation
and the presence of fat droplets in the liver of rats and dogs exposed
to 25 to 100 ppm for 100 days, and fatty degeneration in the liver of
monkeys exposed to 1,000 ppm for 100 days. However, the liver effects
reported in this study were elicited upon continuous exposure. Male and
female Sprague-Dawley rats exposed to DCM (0, 50, 200, or 500 ppm) for 2
years showed an increased incidence of multinucleated hepatocytes at
500 ppm (Nitschke et al. 1982). Exposure to DCM (1,000 ppm-low dose.
-------
Toxicological Daca 57
Table 4.6. Longer-term methyleoe chloride inhalation
exposures and effects in animals
Concentration
(ppm)
5.000
10.000
1,000
5,000
100
25 and 100
25 and 100
1,000 ppm
100
25
100
500
50, 123. 250*'b
500. 1.500. or
3.500
1.000 or
4,000
Duration
7 h/day.
5 days/week
up to
6 months
4 h/day.
5 days/week.
18 weeks
14 weeks
continuous
14 weeks
continuous
100 days
100 days
100 days
100 days
90 days
14 weeks
continuous
10 weeki
continuous
2 yean
2 yean
2 yean
2 yean
Effects
Various experimental animals —
no effect
Various animals — mcoordination.
conjunctiva! irritation:
shallow respiration, pulmonary
congestion, edema with focal
extravasation of blood, some
fatty degeneration
Various experimental animals —
increased hematocnt, Hgb.
RBC, bihrubin. weight loss:
mild centnlobular fat
High mortality: pneumonia:
fatty liver, icterus: splenic
atrophy; edema of meninges;
renal tubule vascular changes
Mice — liver cytoplasmic
vacuolization and positive
fat staining
Rats — nonspecific renal tubular
degenerative and regenerative
changes
Dogs — mild cytoplasmic vacuolation and
sinusoidal congestion in the
liver
Rhesus monkeys— centnlobular
fatty degeneration of the liver
Mice — hepatic cytochrome P-450 decreased
and bj increased
Mice — increased activity
Elevated liver fat: decreased
hepatocyte glycogen:
centnlobular fatty
infiltration
Rats — multmucleated hepatocytea
Rats — hepatocellular alteration and
fatty infiltration
Rau — multinucleated hepatocytes:
liver cytoplasmic
vacuolization
Rats — increased hemosiderosu;
cytomegaly and cytoplasmic
vacuolization in the liver
References
Heppel et al
1944
MacEwen et al.
1972
Haun et ai.
1972
Haun et al.
1972
Haun et al
1972
Thomas et al.
1972
Wemstein and
Diamond 1972
Nitschke et al.
1982, 1988
NCA 1982
Burek et al.
1984
NTP 1986
•mg/kg/day.
Route of exposure-drinking water
Source NIOSH 1976: EPA I985a.c.
-------
58 Section 4
4.000 ppm-high dose) was associated with Che increased incidence of
nemosiderosis, cytomegaly, and cytoplasmic vacuolizacion (NTP 1986).
Oral, human. No hepatotoxlcity studies were found in the available
literature on the oral administration of DCM in humans.
Oral, animal. Liver toxicity was also observed following long-tern
exposures by oral administration (Table 4.5). Increased incidence of
foci and areas of cellular alteration were detected in Fischer 344 rats
administered 50 to 250 mg/kg/day DCM in drinking water for 2 years (NCA
1982). Also, fatty liver changes were detected in the 125- and 250-
ragAg/day dose groups at 78 and 104 weeks of treatment. No liver effects
were observed at 5 mg/kg/day (NCA 1982).
Dermal, human. No hepatotoxicity studies were found in the
available literature on the dermal administration of DCM in humans.
Dermal, animal. No hepatotoxicity studies were found in the
available literature on the dermal administration of DCM in animals.
Discussion. Based on available data, histomorphological changes of
the liver can occur following short-term inhalation exposure (6 h to 7
days) at high dose levels (5,200 ppm). Alteration in cytochrome activity
can occur at lower levels (500 ppm for 10 days). Following longer-term
exposure, liver effects may occur at concentrations greater than 100 ppm
(100 days) following continuous inhalation exposure, and greater than 50
mg/kg/day via ingestion (for 2 years). Animal data presented liver
effects that consisted primarily of histologic alterations of liver
cells, such as those seen in aging animals. Further, the fatty changes
reported were reversible. Liver toxicity was not reported in
epidemiological studies. Therefore, it appears that DCM will not cause
serious liver effects in humans at the higher levels reported in
occupational settings.
4.3.3.4 Renal effects
Available studies show that DCM may cause kidney effects such as
congestion and tubular changes.
Inhalation, human. Several epidemiological studies were conducted;
however, no association was found between DCM exposure and adverse
kidney effects (Friedlander et al. 1978, Ott et al. 1983a, Heame et al.
1987).
Inhalation, animal. No data were found in the available literature
on the renal toxicity of DCM following short-term exposure. However,
continuous exposure to DCM (25 and 100 ppm) for 100 days via Inhalation
in rats shoved nonspecific renal tubular degenerative and regenerative
changes; no changes in organ-body weight ratios were found (Haun et al.
1972) (Table 4.5). These effects were elicited upon continuous exposure
to DCM.
Oral, human. No renal studies were found in the available
literature on the oral administration of DCM in humans.
Oral, animal. No renal studies were found in the available
literature on the oral administration of DCM in animals.
-------
Toxicological Data 59
Dermal, human. No renal studies were found in the available
literature on the dermal administration of DCM in humans.
Dermal, animal. No studies were found in the available literature
on the renal effects of dermally applied DCM in animals.
Discussion. The paucity of data on renal effects in humans and
animals precludes any determination of the significance of this
biological end point as a factor in the toxicity of DCM.
4.3.3.5 Respiratory effects
Available data show that DCM may affect the respiratory system.
Irritant effects were primarily reported.
Inhalation, human. Exposure to DCM in the range of 100 ppm
appeared to cause significant upper respiratory irritation (Velch 1987).
Inhalation, animal. No studies were found in the available
literature on the respiratory effects of inhalation exposure to DCM in
animals.
Oral, human. No studies were found in the available literature on
the respiratory effects of inhalation exposure to DCM in humans.
Oral, animal. No studies were found in the available literature on
the respiratory effects of orally administered DCM in animals.
Dermal, human. No studies were found in the available literature
on the respiratory effects of dermally applied DCM in humans.
Dermal, animal. No studies were found in the available literature
on the respiratory effects of dermally applied DCM in animals.
Discussion. The paucity of data on the respiratory effects of DCM
in humans precludes any determination of the significance of this
biological end point as a factor in the toxicity of DCM.
4.3.3.6 Cardiovascular
Effects on the cardiovascular system were noted in animals,
particularly at high dose levels. In humans, certain individuals with an
existing cardiac disease may be more susceptible to the toxic effects of
DCM.
Inhalation, human. Ott et al. (1983b) reported on SO employees of
two fiber production plants who were selected for study--24 of whom were
occupationally exposed to DCM. All of the participants were white males
between 37 and 63 years of age. Eleven of the men had reported a history
of heart disease. Under the conditions of this study, neither an
increase in ventricular or supraventricular ectopic activity nor
episodic ST-segment depression was associated with exposure to DCM that
ranged from a TWA of 60 to -475 ppm.
Inhalation, animal. Myocardial contractility was altered following
short-term exposure to DCM, usually at concentrations >20,000 ppm
(Aviado and Belej 1974). No data were found on long-term exposures.
-------
60 Section 4
Oral, human. No studies were found in the available literature on
the cardiovascular effects of orally administered DCM in humans.
Oral, animal. No studies were found in the available literature on
the cardiovascular effects of orally administered DCM in animals.
Dermal, human. No studies were found in the available literature
on the cardiovascular effects of dermally applied DCM in humans.
Dermal, animal. No studies were found in the available literature
on the cardiovascular effects of dermally applied DCM in animals.
Discussion. Methylene chloride produces cardiotoxic effects;
however, these effects are most likely mediated by CO via CO-Hb. Data
from experimental exposure studies indicate that blood CO-Hb levels,
following exposure to DCM, are elevated in a manner that is dependent on
the inhaled concentration of DCM and the length of exposure. Exposure to
DCM at concentrations that do not exceed the current OSHA standard of
500 ppm (1,740 mg/m3), as an 8-h TWA with a ceiling of 1,000 ppra and a
maximum peak of 2,000 ppm (5 min in 2 h), can elicit CO-Hb levels of
about 3 to 6%. Exposures at a higher concentration, 1,000 ppm for up to
2 h, result in CO-Hb levels of up to 10%.
The reported CO-Hb concentrations of 3 to 10%, although not
expected to cause adverse health effects in normal healthy individuals
from occasional product use, may be of concern to certain sensitive
populations such as those with compromised cardiovascular systems.
Moreover, since CO is known to bind to myoglobin and disrupt metabolism,
this could affect cardiac function, especially with underlying heart
disease.
4.3.3.7 Ocular effects
Exposure of rabbits to vapors of DCM (17,500 mg/m3) resulted in
increased corneal thickness and intraocular tension (Ballantyne et al
1976).
4.3.4 Developmental Toxicity
4.3.4.1 Overview
Limited studies found in the available literature suggested that
when DCM was inhaled at concentrations of 1,250 ppm and above, it was
developn»ntally and maternally toxic.
4.3.4.2 Inhalation
No developmental toxicity studies were found in the
available literature on the inhalation of DCM in humans.
Animal. Studies have demonstrated that DCM crossed the placental
barrier (Anders and Sunram 1982). Fetuses of Swiss-Webster mice and
Sprague-Dawley rats exposed to DCM (1,250 ppm) on days 6 to 15 of
gestation showed cleft palate and rotated kidneys (mice), dilated renal
pelvis (rats), and delayed ossification of sternebrae (mice and rats)
(Schwetz et al. 1975). These effects were not statistically significant
except for a minor skeletal variant (extra sternebrae, P < 0.05).
Developmental toxicity, as evident by Lowered fetal body weights, was
-------
Toxicological Daca 6L
reported in rats at 4,500 ppm (-15,600 mg/m3) (Hardtn and Hanson 1980)
It should be noted that these effects were also observed at minimally
maternally toxic levels. In rats exposed to 1,250 ppm, the average
absolute maternal liver weight was significantly increased over control
levels (Schwetz et al. 1975). In mice, there was a significant increase
in maternal body weight and absolute liver weight at 1,250 ppm (Schwetz
et al. 1975). Maternal toxicity, manifested by increased absolute and
relative liver weights, was reported in rats at 4,500 ppm. Malformations
in chick embryos were reported when DCM was injected into the air sacs
of fertile eggs (Elovaara et al. 1979). The significance of these
malformations and their relevance to mammalian teratology is unclear.
4.3.4.3 Oral
Human. No studies were found in the available literature on the
developmental toxicity of orally administered DCM in humans.
Animal. No studies were found in the available literature on the
developmental toxicity of orally administered DCM in animals.
4.3.4.4 Dermal
Human. No studies were found in the available literature on the
developmental toxicity of dermally administered DCM in humans.
Animal. No studies were found in the available literature on the
developmental toxicity of dermally administered DCM in animals.
4.3.4.5 Discussion
The practical importance of these findings is limited since each of
the two studies used only one dose level, and these effects were
observed at a maternally toxic dose. Further, the effects on fetal
development in mice were minor. The use of only one dose level precludes
any evaluation or dose-response relationships. Evidence, therefore, does
not currently exist to conclusively characterize the developmentally
toxic potential of DCM.
4.3.5 Reproductive Toxicity
4.3.5.1 Inhalation
Human. No reproductive toxicity studies were found in the
available literature on the inhalation of DCM in humans.
Aniaal. No adverse effects on reproductive parameters, neonatal
survival, or neonatal growth were observed in F344 rats exposed to 0,
100, 500, or 1.500 ppm DCM for 6 h/day, 5 days/week for 14 weeks in
either FO or Fl generations (Nitschke et al. 1985). Similarly, there
were no treatment-related gross pathological effects on FQ and Fl adults
and Fl and F2 weanlings at necropsy. Histopathological examination of
tissues from Fl and F2 weanlings did not reveal any lesions attributed
to DCM toxicity.
-------
62 Section 4
4.3.S.2 Oral
Human. No studies were found In the available literature on the
reproductive effects of orally administered DCM In humans.
Animal. When DCM (125 ppm) was administered in the drinking water
of male and female rats for 91 days, there were no effects on the estrus
cycle or on reproduction (Bornmann and Loesser 1967).
4.3.5.3 Dermal
Human. No studies were found In the available literature on the
reproductive effects of dermally applied DCM in humans.
Animal. No studies were found in the available literature on the
reproductive effects of dermally applied DCM In animals.
4.3.5.4 Discussion
Only one study (two-generation) was found In the available
literature that evaluated end points acceptable for assessing
reproductive toxicity. The results of this study were negative. Based on
these data, DCM does not appear to pose a hazard to human reproduction.
4.3.6 Genotoxicity
The genotoxicity of DCM has been evaluated in a variety of
mammalian test systems (in vitro and in vivo) in studies by Andrae and
Wolff 1983; Burek et al. 1984; CEFIC 1986c,d,e; Gocke et al. 1981;
Jongen et al. 1981; McCarroll et al. 1983; Perocco and Prodi 1981; and
Thilagar and Kumaroo 1983, 1984a,b. Results of these studies are
summarized in Table 4.7. Methylene chloride reportedly produced a dose-
related increase in chromosomal aberrations in human peripheral
lymphocytes, in Chinese hamster ovary (CHO) cells, and In mouse lymphoma
L5178Y cells. Methylene chloride was tested in CHO cells at 2, 5, and 10
/iL/mL in the presence and absence of an S9 system and at 15 /*L/mL in the
presence of the system (Thilagar and Kumaroo 1983). Chromosome damage
occurred at all dose levels, and the extent of damage was greater in the
presence of activation. Maximum levels of chromosome damage were
obtained in the presence of S9 at the highest DCM concentration (15
ML/mL) (Thilagar and Kumaroo 1983). In a study of human peripheral blood
lymphocytes, DCM again induced chromosome aberrations in the presence
and absence of a metabolic activation system when tested at 1 to 5 pL/mL
(-S9) and at 2 to 6 /*L/mL (+S9). No evidence of chromosome abnormalities
were seen in bone marrow cells of rats exposed by inhalation to 500,
1,500, or 3,500 ppm DCM for 6 h/day, 5 days/week for 6 months (Burek et
al. 1980). When DCM was evaluated to assess its potential to induce
sister chromatid exchanges (SCE), negative results were obtained
following 2-, 4-, and 10-h exposures (McCarroll et al. 1983). Following
a 24-h exposure to a 1.8, 3.6, 5.4, or 7% (DCM/air, v/v) atmosphere,
dose-related increases (? < 0.01) of SCE were obtained at the 7% dose
level (McCarroll et al. 1983). An additional study (Jongen et al. 1981)
reported a weak effect on SCE induction, which reached a plateau at the
1% dose level. Exposure to concentrations as high as 4% over 1, 2, and
4 h with and without an S9 fraction did not increase the rates of SCE
above those seen at 1%.
-------
lexicological Data 63
Table 4.7. Results of mettaylcw chloride
Bf in tartan
short-tcfB tests
End point
Target cell
Result"
Reference*
Chromosome aberrations Human peripheral lymphocytes
CHO cells
Mouse lymphoma L5178Y
Rat bone marrow (microsomes)
Sister chromatid exchange Human peripheral lymphocytes
CHO cells
Thilagar et al. 1984a
Burek et al. 1984
Thilagar et al. 1984b
V79
Mouse lymphoma L5178Y
Point mutations L5178Y/TK
CHO/HGPRT
V79/HGPRT
DNA damage and repair Primary rat hepatocytes
Human penpheral lymphocytes
Primary human fibroblastt (AH)
V79
In vivo/in vitro rat hepatocytes
Micronucleus
In vivo/in vitro mouse hepatocytes
Mouse bone marrow
Thilagar et aL 1984
Jongen et aL 1981
CEFIC 1986c
Perocco and Prodi 1981
CEFIC 198«e
CEFIC I986d
Gocke et aL 1981
CEFIC I986e
a-f — positive, — — negative, ± • margmaL
-------
64 Section 4
Methylene chloride was not mutagenic In three studies utilizing
several mammalian cell systems. Metabolic activation was used. Mechylene
chloride did not induce unscheduled DNA synthesis (UDS) in two of three
studies with primary rat hepatocytes (Andrae and Wolff 1983, CEFIC
1986c). A positive response was only marginal in the third study
(Thilagar et al. 1984b). Methylene chloride was also negative in UDS
studies in primary mouse hepatocytes, human peripheral lymphocytes,
primary human fibroblasts, and V79 cells. When rats or mice were exposed
to 2000 or 4000 ppm DCM by inhalation for either 2 or 6 h, no UDS was
detected in either species (CEFIC 1986c). Methylene chloride did noc
induce micronuclei in mouse bone marrow cells following two
intraperitoneal administrations (at 0 and 24 h), with smears being
prepared at 30 h (Gocke et al. 1981). Methylene chloride did not induce
a biologically or statistically significant increase in polychromatic
erythrocytes containing micronuclei when tested orally in corn oil at
dose levels of 4,000, 2,500, and 1,250 mg/kg in C57BL/6J/ALpk mice
(CEFIC 1986e). The induction of S-phase hepatocytes in B6C3F1 mouse
liver was measured after one or two inhalation exposures to 4,000 ppm
DCM for 2 h (CEFIC 1986d). The author reported small, but statistically
significant, increases in the number of S-phase cells. Since the
induction of S-phase hepatocytes is not a commonly used assay, the
usefulness of these findings is limited. Results were equivocal in UDS
studies conducted in vitro (CEFIC 1986c).
The in vivo interaction of DCM and its metabolites with F344 rat
and B6C3F1 mouse lung and liver DNA was measured after inhalation
exposure of 4,000 ppm 14C-DCM for 3 h (CEFIC 1986b). The DNA was
isolated from the tissues 6, 12, and 24 h after the start of exposure
and then analyzed for total radioactivity and the distribution of
radioactivity within enzymically hydrolysed DNA samples. Covalent
binding to hepatic protein was also measured. An additional-group of
rats and mice were dosed intravenously with ^C-formate (after exposure
to nonradiolabeled DCM for 3 h) to determine the pattern of labeling
resulting from the incorporation of formate into DNA via the C-l pool.
Low levels of radioactivity were found in DNA from the lungs and livers
of both rats and mice exposed to 14C-DCM. Two- to fourfold higher levels
were found in mouse DNA and protein than in the rat. Chromatographic
analysis of the DNA nucleosides showed the radioactivity to be
associated with the normal constituents of DNA. No peaks of
radioactivity were found that did not coincide with peaks of
radioactivity present in hydrolysed DNA from formate-treated rats and
mice. Under the conditions of this study, there was no evidence for
alkylation of DNA by DCM, and it was concluded that DCM was not
genotoxic (CEFIC 1986b).
There is clear evidence of mutagenicity in bacteria. Results were
mixed in tests of yeast, drosophila, and mammalian cells in cultures,
and were largely negative in mammalian cells in vivo. Given the evidence
of in vitro clastogenicity DNA binding studies, it was concluded that
DCM may be a weak mutagen in mammalian systems (EPA 1987a,b).
-------
Toxicologies! Data 65
4.3.7 Carcinogeniclty
4.3.7.1 Overview
Two cohort studies examined the mortality incidence in workers
occupationally exposed to DCM. Neither study reported a statistically
significant increase in deaths from cancer among workers exposed to DCM
These occupational studies are not adequate to rule out a risk of cancer
to humans from DCM, and the compound should be regarded as though it has
some potential to cause cancer. Carcinogenic responses were reported in
various animal studies following inhalation and ingestion of DCM. Lung
and liver tumors were reported in mice of both sexes following exposure
through inhalation for lifetime. Inhalation studies involving rats and
hamsters revealed sarcomas in the salivary gland region of male rats,
but no malignant responses were reported in female rats and in hamsters
of both sexes. The authors suggested that a salivary gland viral disease
in rats may have contributed to the development of the tumorigenic
response. Rats of both sexes have shown an elevated incidence of benign
mammary tumors. Some liver tumors were produced in rats and mice that
ingested DCM in drinking water for 2 years, but the tumor incidences
were not considered by the authors to be compound related. These
responses were considered by EPA to be borderline evidence of
carcinogenicity. Based on the weight of evidence from these animal
studies, and applying the criteria described in EPA's guidelines for
assessing carcinogenic risk (EPA 1986c), DCM was classified in Group B2:
probable human carcinogen (EPA 1985b).
4.3.7.2 Human
Data were found in the available literature for inhalation
exposure, but not for the oral or dermal administration of DCM.
Friedlander et al. (1978) analyzed mortality statistics for male
workers exposed to low levels of DCM. Measurements from 1959 to 1976
were TWA concentrations in the range of 40 to 120 ppm (estimated), both
from air monitoring and blood CO-Hb levels for up to 30 years. No excess
cancer mortality was found compared with the unexposed population.
Hearne et al. (1987) evaluated an expanded employee cohort for cancer
mortality. A maturing 1964 to 1970 cohort of 1,013 hourly men were
evaluated through 1984. On average, employees were exposed at a rate of
26 ppm for 22 years (median latency was 30 years). Compared with the
general population, no statistically significant excesses were observed
in deaths from malignant neoplasms (41 observed vs 52.7 expected), from
respiratory cancer deaths (14 vs 16.6), or from liver cancer deaths (0
vs 0.5). An increased incidence of pancreatic cancer deaths (8 vs 3.1
expected) was reported; however, these deaths were not considered to be
statistically significant (Hearne et al. 1987). Ott et al. (1983a)
evaluated cancer mortality among employees of a fiber production plant
who were exposed to TWA concentrations of 140 to 475 ppm. They observed
fewer than expected deaths from malignant neoplasms in comparison to
expected deaths from the same cause in the general population.
-------
66 Section 4
4.3.7.3 Animal
Several studies were found in the available literature that
demonstrated the carcinogenic potential of DCM (Table 4.8). Risk
estimates were conducted by EPA based on the occurrence of liver and
lung tumors following the inhalation of DCM by mice (NTP 1986) and on
suggestive evidence in mice (NCA 1983) following the ingestion of
DCM-contaminated drinking water. The NTP (1986) reported that in mice
exposed co DCM, the incidence of hepatocellular carcinomas alone was
statistically increased over controls in high-dose males (P - 0.005) and
in both high-dose females (P < 0.001) and low-dose females exposed to 0
(male 13/50, female 1/50), 2000 (male 15/49, female 11/48), and 4,000
ppm (male 26/49, female 32/48) for 102 weeks. The incidence of combined
hepatocellular adenomas and carcinomas in the 4,000-ppm group of male
mice (33/49) was significantly (P - 0.02) higher than controls (22/50).
There were also increased incidences in the low-dose (16/48, P < 0.001)
and high-dose (40/48, P < 0.001) females when compared with controls
(3/50).
Methylene chloride induced a dose-dependent statistically
significant increase in lung adenoma and carcinoma in mice of both sexes
exposed through inhalation for 2 years (NTP 1986). Tumor incidences were
as follows: at 2,000 ppm, 30 of 48 female mice and 27 of 50 male mice
developed lung tumors compared with 3 of 50 (female) and 4 of 50 (male)
in the control groups. At 4,000 ppm, 41 of 48 female mice and 40 of 50
male mice developed lung tumors.
The NCA (1983) evaluated the carcinogenicity of ingested DCM in
B6C3F1 mice from drinking water at doses of 0, 60, 125, 185, or 250
ing/kg/day £°r 104 weeks. The incidence of proliferative hepatocellular
lesions was higher in treated males than in male control groups (but not
in females); however, the increase was reported not to be dose related
or statistically significant when ompared with concurrent control
rates. In addition, the incidence of lesions in treated groups was
within the historical range of control values. It was concluded,
therefore, that DCM did not induce a carcinogenic response under the
study conditions. An independent assessment of the NCA (1983) data by
the EPA (1985a) concluded that the incidence of heptocellular adenomas
and carcinomas (combined) was significantly (P < 0.05) increased in male
B6C3F1 mice exposed to 125 mg/kg/day (30/100) or 185 mg/kg/day (31/99)
of DCM in drinking water when compared with controls (24/125). The EPA
(1985a) concluded that, on the basis of the increased incidence observed
in the NCA study, DCM administered in deionized drinking water at doses
up to 250 mg/kg/day produced borderline carcinogenicity in B6C3F1 male
mice.
In a rat study (NCA 1982), DCM was administered in drinking water
to both sexes at 0, 5, 50, 125, and 250 mg/kg/day for 104 weeks. An
increase in liver tumors was reported in females treated at 50 and 250
ngAg/day when compared with concurrent controls. These levels were
within historical control ranges. The authors concluded that DCM was not
carcinogenic under conditions of the study. The EPA (1985a) evaluated
results of the study and reported an increased incidence of neoplastic
nodules combined with hepatocellular carcinomas in female rats
-------
Toxicologies! Data 67
Table 4.8. Summary of primary tumors in rats and mice
in 2-year studies of methyleoe chloride
Route Species
Strain
Concentration
Tumor site
References
Inhalation
Inhalation
Drinking
water
Drinking
water
Inhalation
Inhalation
Hamster
Rat
Rat
Mouse
Rat
Mouse
Syrian
Sprague-Dawley
F344
B6C3F,
F344/N
B6C3F,
0, 500, 1,500,
3,500 ppm
0, 50, 200,
500 ppm
0, 5, 50, 125,
250 mg/kg
0, 60, 125,
185, 250 mg/kg
0, 1,000, 2,000,
4,000 ppm
0, 2.000,
4,000 ppm
No reported
effect
Mammary gland
(females)
Liver
(female)
Liver
(male)
Mammary gland
(both sexes)
Liver and lung
(both sexes)
Nitschke et al."
1982
National Coffee
Association 1982
National Coffee
Association 1983
National
Toxicology
Program 1986
•Nitschke efal. 1988.
Source: Adapted from NTP 1986.
-------
68 Section 4
(P < 0.05) when compared with matched controls. Tumor incidences were as
follows 0/134, 1/85, 4/85, 1/85, and 6/85 in combined control, 5-, 50-,
125-, and 250-mg/kg/day groups, respectively. The EPA (1985a) concluded
that based on the combined incidence of adenomas and carcinomas, DCM
showed borderline evidence of carcinogenicity in rats when administered
orally.
Burek et al. (1980, 1984) exposed rats and hamsters of both sexes
to DCM (0, 500. 1,500, or 3,500 ppm) via inhalation for 2 years.
Sarcomas in the salivary gland region of male rats were reported at
1,500 or 3.500 ppm. This effect was statistically significant in the
3,500-ppm group, with a trend (numerically increased but not
statistically significant) for an increase in the 1,500-ppm group. The
toxicological significance of this finding is unknown. Results were
negative for female rats and for hamsters of both sexes. The authors
suggested that a salivary gland viral disease in rats may have
contributed to the tumorigenic response.
Rats of both sexes were administered DCM (at doses of 0, 50, 200,
or 500 ppm) via inhalation for 2 years (Nitschke et al. 1982, 1988).
Female rats exposed to 500 ppm had an increased (P < 0.05) number of
spontaneous benign mammary tumors (tumor-bearing rat adenomas, fibromas,
and fibro adenomas, with no progression toward malignancy). The
incidence of benign mammary tumors in female rats exposed to 50 or 200
ppm was comparable to historical control values. No increase in the
number of any malignant tumor types was observed in rats exposed to
concentrations as high as 500 ppm DCM.
4.4 INTERACTIONS WITH OTHER CHEMICALS
Limited studies were found in the available literature on the
interactions of DCM with other chemicals. Much of the data found focused
on concurrent exposure to carbon monoxide, since DCM is metabolized to
carbon monoxide. In rats, combined carbon monoxide and DCM exposure
yielded additive increases in the carboxyhemoglobin levels (ACGIH 1986)
Fodor and Roscavanu (1976) reported that exposure of human subjects to
500 ppm of DCM resulted in levels of carboxyhemoglobin in the blood
comparable with those produced by the Threshold Limit Value for carbon
monoxide (50 ppm). Because carbon monoxide generated from DCM is
additive to exogenous environmental carbon monoxide, DCM exposures at
high levels could pose an additional human health burden. Of particular
concern are workers, smokers (who maintain significant constant levels
of carboxyhemoglobin), and others who may have increased sensitivity to
carbon monoxide toxicity, including persons with cardiovascular disease
and respiratory dysfunction.
-------
69
5. MANUFACTURE. IMPORT, USE, AND DISPOSAL
5.1 OVERVIEW
Approximately 265,000 megagrams (Mg) of DCM were produced in the
United States in 1983 at six major production plants in four states.
After accounting for imports and exports, about 252,000 Mg were
available for U.S. consumptive use (50 FR 42037).
The major uses of DCM are in aerosol products and as a paint
remover, which together account for more than 50% of the DCM used in the
United States in 1983.
Although data on land disposal of DCM from production processes
were not available, it appears that land disposal is not a major source
of the DCM released to the environment.
5.2 PRODUCTION
Methylene chloride is produced in the United States by two major
processes. The methane chlorination process combines methane and
chlorine in a closed reactor. The DCM and carbon tetrachloride are
separated from the reaction mixture by distillation. The second process,
chlorination of methyl chloride, combines methyl chloride (formed by
reaction of hydrogen chloride with methanol) and chlorine in a reactor
vessel. The process flow is passed through a hydrochloric acid stripper
Both these processes allow recycling of hydrochloric acid (OSHA 1986,
HSDB 1987).
There were four major producers of DCM in the United States in
1983, with plants at six locations in four states (Texas, West Virginia,
Louisiana, -and Kansas). The total 1983 production volume was
approximately 265,000 Mg (OSHA 1986, EPA 1985d).
5.3 IMPORT
In 1983, 20,000 Mg of DCM were imported into the United States, and
33,000 Mg were exported (50 FR 42038, OSHA 1986).
5.4 US»
The two major consumptive uses of DCM in the United States in 1983
were as a paint remover and as a solvent and flammability depressant in
aerosol products such as coatings, paint removers, hair sprays, room
deodorants, herbicides, and insecticides. Of the total U.S. production
of DCM in 1983 (265,000 Mg), 69,400 Mg (26.2%) were used in aerosol
products, and 63,100 Mg (23.8%) were used in paint removal products.
Other important uses of DCM include foaa blowing of polyurethanes, mecal
degreasing, stripping and degreasing in the electronics industry, as a
solvent in polycarbonate resin production, in photographic film-base
-------
70 Section 5
manufacturing, adhesive production, and numerous other solvent.
cleaning, and thinning uses. Methylene chloride is also occasionally
used as an extractant for caffeine, spices, and hops (OSHA 1986, HSDB
1987, EPA 1985a).
5.5 DISPOSAL
No data were found on the land disposal of DCM from production
processes. However, it appears that land disposal is not a major route
of the environmental release of DCM (EPA 1985a).
-------
71
6. ENVIRONMENTAL FATE
6.1 OVERVIEW
Methylene chloride is released Co Che environmenc mainly through
its varied and widespread uses. PainC removal, aerosol use, mecal
degreasing, foam blowing, and miscellaneous uses account for"the bulk of
DCM releases. Approximately 85% of the total amount of DCM produced in
the United States is released to all media, primarily in industrialized
areas. Although no estimates of releases to specific media are
available, most is probably released to the air. The chlorination of
drinking water also produces DCM.
Volatilization of DCM occurs from all sources and in all
environmental media. While atmospheric transport and dispersion are
important, degradation by hydroxyl radicals, photolysis, and intermedia
transfer via rainout prevent DCM from accumulating in the atmosphere.
Because of its moderate water solubility, leaching from soil and
transport in groundwater and surface water are important fate processes.
Soil adsorption and abiotic transformation processes in aquatic systems
are not major factors for DCM. Biodegradation may be an important fate
process, but bioaccumulation and bioconcentration are not considered to
be significant factors in aquatic, sediment, and wastewater treatment
systems.
6.2 RELEASES TO THE ENVIRONMENT
6.2.1 Anthropogenic Sources
The major sources of DCM are anthropogenic, as are DCM emissions to
the environment. Although many varied and widespread uses contribute to
DCM emissions, paint removal, aerosol use, metal degreasing, foam
blowing, and miscellaneous uses account for 158,900 Mg/year (about 81%)
of the -196,000 Mg/year released (50 FR 42037, Oct. 17. 1985). These
releases occur primarily to sewage treatment plants, surface water,
land, and the atmosphere (EPA 1985a).
Losses during production, transport, and storage are primarily
fugitive (e.g., from leaky Joints, values, and pump seals). These losses
are poorly documented; however, they are considered to be a small
percentage of the total emissions from other uses (EPA 1985a).
The maximum concentration measured in industrial wastewater
(210 ppm) is associated with discharges by the paint- and ink-
formulating and aluminum-forming industries (EPA 1981a, as cited in HSDB
1987). Other industries in which concentrations of DCM exceed an average
discharge concentration of 1 ppm include coal mining, photographic
equipment and supplies, pharmaceutical manufacturing, organic chemical
and plastics manufacturing, rubber processing, and laundries. Methylene
-------
72 Section 6
chloride is produced in drinking water (in Che low parts-per-billion
concentration range) during chlorination treatment (NAS 1977 Bellar et
al. 1974, as cited in EPA 1985a).
6.2.2 Natural Sources
Methylene chloride may be formed from natural sources, but these
are not believed to contribute significantly to global releases (NAS
1978, as cited in EPA 1985d).
6.3 ENVIRONMENTAL FATE
6.3.1 Atmospheric Fate Processes
Methylene chloride released to the atmosphere is expected to
readily disperse and be transported some distance from its source. It is
not expected to accumulate significantly in the atmosphere, however.
because of the reaction with hydroxyl radicals (OH-). This reaction is
considered the primary tropospherlc chemical scavenging process for DCM
(EPA 1985a). Based on reaction rate studies summarized by the EPA
(1985a), the lifetime of DCM in the troposphere ranges from a minimum of
a few months to a maximum of 1.4 years under typical U.S. conditions
(Altshuller 1980; Cox et al. 1976; Crutzen and Fishman 1977; Davis et
al. 1976; Singh 1977; Singh et al. 1979, 1983). Most estimates of how
long DCM lingers in the atmosphere are less than a year, suggesting
atmospheric accumulation is not important, whereas dispersive transport
is a matter of concern.
Butler et al. (1978, as cited in EPA 1985a) proposed that the
reaction of DCM and OH- may form phosgene (COC12) as a degradation
product. The small amount of DCM that reaches the stratosphere (about
1%) will degrade via photolysis and reaction with chlorine radicals
(HSDB 1987). The highest concentrations of DCM have been observed at
night and in early morning (Singh et al. 1982, as cited in HSDB 1987),
which suggests that photooxidation may be an important degradation
process. Pearson and McConnell (1975) reported on laboratory studies
that show that the photolysis of DCM may yield O>2 and hydrochloric
acid.
6.3.2 Surface Vater/Groundvater Fate Processes
Volatilization is the most important fate process In surface
waters, whereas transport is likely to be important in groundwater,
considering DCM's moderate water solubility. Dewalle and Chian (1978)
and Helz and Hsu (1978) (as cited in HSDB 1987) reported DCM as
nondetectable 3 to 15 miles downstream from where it had been released
into a river. The rate of volatilization from surface water is expected
to be strongly affected by wind and mixing conditions.
Biodegradation may be an important fate process under both aerobic
and anaerobic conditions. Hydrolysis occurs slowly in this medium and LS
strongly influenced by pH and temperature. Studies cited by EPA (1985c)
indicate an estimated half-life of 18 months at 25°C.
-------
Environmental Face 73
6.3.3 Soil Fate Processes
Volatilization, leaching, and biodegradation are expected to be
important fate processes for DCH in soil. Adsorption to soil is not
expected to be important (Dilling et al. 1975, as cited in EPA 198Sc).
6.3.4 Biotic Fate Processes
The EPA (198Sa) cites a number of studies indicating the microbial
(e.g., Pseudomonas spp.) biodegradation of OCM in aquatic systems
(Brunner et al. 1980, Lapat-Polasko et al. 1984, Rittman and HcCarty
1980, Klecka 1982, Wood et al. 1981). Breakdown appears to yield methyl
chloride as an intermediate and C02 as the final carbon-containing end
product. Modeling indicates the biodegradation rate is about 12 times
greater (in a continuously stirred activated sludge reactor containing
acclimated microorganisms) than the volatilization rate (Klecka 1982, as
cited in EPA 198Sa). HSDB (1987) reports biodegradation rates for sewage
seed or activated sludge ranging from 6 h to 7 days under aerobic
conditions, based on results of five studies (Davis et al. 1981, Klecka
1982, Rittman and HcCarty 1980, Stover and Kincannon 1983, Tabak et al.
1981).
Hansch and Leo (1979, as cited in HSDB 1987) report a low
octanol/vater partition coefficient for DCM (log P - 1.25), suggesting
bioaccumulation and bioconcentration are not important fate processes.
-------
75
7. POTENTIAL FOR HUMAN EXPOSURE
7.1 OVERVIEW
Host human exposure to DCM occurs via air. Air exposures are
highest in occupational settings and near sources of emissions.
Inhalation exposures are also higher in industrialized urban areas.
There is a potential for low-level general population exposure from
ambient DCM emissions from paint removal, aerosol use, metal degreasing,
electronics, Pharmaceuticals, food processing, and miscellaneous uses.
Hazardous waste sites release DCM to the air, groundwater, and surface
water. Very low levels of DCM exposure occur through ingestion of
decaffeinated coffee. Monitoring data on DCM exposure levels outside of
occupational settings are sparse.
Populations at elevated risk for*exposure to high concentrations of
DCM are individuals in occupational settings in the following industrial
categories: DCM manufacturing, paint remover formulation, polycarbonate
resin production, and cleaning solvent. Consumers may be exposed to
significant amounts of DCM vapors through the use of a variety of
products. These are summarized in Sect. 7.4.
7.2 LEVELS MONITORED OR ESTIMATED IN THE ENVIRONMENT
7.2.1 Levels in Air
Methylene chloride occurs in ambient air throughout the United
States, with background levels reported in a number of studies falling
in the range of 30 to 50 ppt (Brodzinsky and Singh 1983, Cronn et al.
1977, Cronn and Robinson 1979, Grimsrud and Rasmussen 1975, Rasmussen et
al. 1979, Robinson 1978, Singh et al. 1983, as cited in EPA 1985a).
Measured ambient air levels (as mixing ratios) of DGM (Grimsrud and
Rasmussen 1975; Pellizzari 1977, 1978a, 1978b; Pellizzari and Bunch
1979; Pellizaari et al. 1979; Rasmussen et al. 1979; Singh et al. 1979,
1980, 1981) are summarized by the EPA (1985a). The data confirm maximum
and mean concentrations in urban areas are the highest, with Front
Royal, Virginia, and Edison, New Jersey, having the highest values for
urban areas.
Pellizzari and Bunch (1979, as cited in EPA 1985a) reported the
highest ambient air level of DCM in a New Jersey survey to be 360 ppb.
Measurements were made during an 11-min sampling period at a waste
disposal site in Edison. Harkov et al. (1985) reported average air
concentrations of DCM at six abandoned hazardous waste sites and at one
sanitary landfill in New Jersey to fall in the range of 0.1 to 12.3 ppb,
with a maximum measured concentration of 53.8 ppb.
-------
76 Section 7
7.2.2 Levels in Water
Methylene chloride occurs in drinking water, surface water, and
groundwater throughout the United States. Six of seven studies reviewed
by EPA (1985d) reported the presence of DCM in drinking water (Bellar et
al. 1974; Coleman et al. 1976; Dowty et al. 1975; Pellizzari and Bunch
1979; EPA 1975a, 1975b). Mean reported concentrations in finished
drinking water were around 1 pg/L or less, with maximum concentrations
reported at <3 A»g/L. Bellar et al. (1974, as cited in EPA 1985a)
reported 2.0 ng/L DCM in finished water produced from raw river water
containing no detectable DCM. Dyksen and Hess (1982, as cited in HSDB
1987) reported that 2% of the drinking water samples in a ten-state
survey of groundwater supplies were positive for DCM, with a maximum
reported concentration of 3.6 ppm. Methylene chloride also occurs in
commercially bottled artesian well water (Dowty et al. 1975, as cited in
EPA 1985a).
Ewing et al. (1977, as cited in EPA 1985a) reported DCM at
concentrations greater than 1 ppb in 32 of 204 surface water sites
sampled in heavily industrialized river basins. Pellizzari and Bunch
(1979, as cited in EPA 1985a) reported a mean DCM concentration of 2.6
Pg/L and a maximum of 15.8 pg/L in untreated Mississippi River water in
Jefferson Parrish, Louisiana. The EPA (1981b, as cited in EPA 1985a)
reported DCM levels in EPA's automated database (STORET) files for the
period 1978 to 1981 to range from 0 to 120 /ig/L in general ambient
waters. Sediment concentrations were in the range of 427 to 433 ppb in
60 of 118 cases. Values in surface waters from the Ohio River Valley and
Great Lakes region fall in the range of 1 to 30 ppb (ORVWSC 1982,
Konasewich et al. 1978, as cited in HSDB 1987). Most of the samples with
detected concentrations of DCM from the Ohio River Valley (219 of 238)
were below 10 ppb.
Methylene chloride has been detected in groundwater at levels up to
8.4 mg/L at 36 Superfund hazardous waste sites and in surface water at
17 other waste sites. Methylene chloride is ranked 16th of the 25
substances most frequently detected at the 53 Superfund sites sampled by
EPA (1985e and 1985f, as cited in 50 FR 42037, Oct. 17, 1985).
7.2.3 Levels in Soil
The EPA (1981b, as cited in EPA 1985a) reports that measurements of
ambient DCM soil concentrations (for areas not associated with hazardous
waste sites) are not available.
7.2.4 Levels in Food
Information on levels of DCM in food is generally not available.
The Food and Drug Administration has placed a limit of 10 ppm DCM for
decaffeinated coffee (50 FR 51551, Dec. 18. 1985). Measured amounts are
significantly less than this limit.
7.2.5 Resulting Exposure Levels
The highly variable atmospheric concentrations of DCM in different
areas make any quantitative estimates of exposure levels highly
-------
Potential for Human Exposure 77
speculative and somewhat meaningless. Exposures from drinking water
(being more relevant to hazardous waste site environmental contamination
situations) can be roughly estimated from data summarized earlier. The
mean concentration of DCM in finished drinking waters (from all sources)
was reported at about 1 pg/L with maximum concentrations <3 /ig/L. This
would result in a daily exposure of about 2 /jg/day (mean) and <6 jig/day
(maximum) for a 70-kg adult with an assumed water consumption of
2 L/day. Since concentrations up to 8.4 mg/L DCM have been detected in
groundwater at hazardous waste sites, an upper range estimate of
localized human exposure is 16.8 mg/day. This estimate assumes that the
sole source of drinking water is the contaminated aquifer, and it is
used directly without treatment for the removal of DCM.
The FDA's limit of 10 ppm DCM in decaffeinated coffee is estimated
to result in a lifetime average exposure of 140 fig/day for consumers of
brewed (roasted and ground) decaffeinated coffee, and 55 pg/day for
consumers of instant decaffeinated coffee (50 FR 51551, Dec. 18, 1985)
Insufficient data are available to estimate exposure from the intake of
other foods.
Occupational inhalation exposure levels are summarized in Sect.
7.3. Data on other exposure levels are not available.
7.3 OCCUPATIONAL EXPOSURES
Occupations in which exposure to DCM may occur are listed in Table
7.1. Nearly 2.5 million workers are estimated to be exposed to DCM
(ICAIR 1985). Highest occupational inhalation exposure levels (1,750
mg/nr*, as an 8-h TWA) occur in the following industrial categories
(Table 7.2): DCM manufacturing (production workers), paint remover
formulation (production filing), and polycarbonate resin production
(production worker) (50 FR 42037, Oct. 17, 1985). The industry-wide 8-h
TWA exposure level is 22.4 ppm (51 FR 42257, Nov. 24,1986). High
exposure concentrations may develop rapidly in poorly ventilated areas.
The EPA (50 FR 42037, Oct. 17, 1985) reports breathing zone exposures of
1,000 to 3,000 ppm DCM in simulated consumer exposure to paint strippers
in a room-sized environmental chamber.
7.4 CONSUMER EXPOSURE
The Consumer Product Safety Commission (CPSC) (1987) reported that
products in the following classes (that contain DCM) can expose
consumers to significant amounts of DCM vapors and are thus hazardous:
paint strippers, adhesives and glues, paint thinners, glass frosting and
artificial snow, water repellants, wood stain and varnishes, spray
paint, cleaning fluids and degreasers, aerosol spray paint for
automobiles, automobile spray primers, and products sold as DCM. The
commission stated that it does not have up-to-date information showing
that products in these categories that contain 1% or less of DCM are
hazardous substances.
-------
78 SeccIon 7
Table 7.1. Occupations in which methylene chloride
exposures may occur
Aerosol packagers
Bitumin makers
Fat extractors
Leather finish workers
Paint remover makers
Solvent workers
Production workers in methylene chloride manufacturing
Mold release workers
Paint strippers
Foam operators in the polyurethane foam blowing industry
Extrusion workers in the triacetate extrusion business
Assemblers and other workers in the plastics industry
Printers and other workers in the printing industry
Maintenance workers
Painters (including spray painters)
Machine operators and assemblers using cleaning solvents
Anesthetic makers
Degreasers
Flavoring makers
Oil processors
Resin makers
Stain removers
Packers in aerosol packing
Production filling and paint remover formulators
Solvent reclaimers
Production workers with pharmaceutical solvents
Production workers in film-base manufacturing
Laminators
Gluers and other workers using adhesives
Plate-makers
Compounders of production solvents
Assemblers and other workers in the electronics industry
Production workers in the polycarbonate resin production industry
Source: ICAIR 1985.
-------
Potential for Human Exposure 79
Table 7.2. Summary of occopadoaal exposure to netayteae chloride
Industry category
Methylene chloride manufacturing
Aerosol packing
Aerosol use
Paint remover formulation
Paint remover use
Polyurethane foam blowing
Metal degreating
Solvent recovery
Pharmaceutical solvent
Triacetate extrusion
Solvent for plastics
Adhesive use
Printing
Production solvent
Electronic
Cleaning solvent
Polycarbonate rain production
Not classified
Job category
Production worker
Packer
Spray painter
Mold release
Other workers
Production Tilling
Paint stnpper
Water wash
Other workers
Foam operator
Other worker
Degreaser
Solvent reclaimer
Production worker
Extrusion
Finish
Other worker
Gluer
Assembler
Other worker
Laminator
Gluer
Other worker
Printer
Plate- maker
Other worker
Compounder
Other worker
Assembler
Other worker*
Maintenance
Painter
Machine operator
Assembler
Production worker
Other worker
Estimated
number of
workers
1.200*
896r
14.296
25.972
50,343
1.280
7.680*
25.60T/
3.840*
405e
162'
227.848
170*
19.046
340
460
120
1.514
984
8.022
1.366
280
901
43,931
15.911
27.531
15,041
1.531
10.399
11.267
49.884
1.831
79.951
22.252
1.200
342,064
1.016,894
8-h TWA
exposure
(mg/m3)"
1.750
317
46
80
28
1.750
57
67
192
51
97
46
13
141
1.479
187
1.036
437
197
21
30
6
15
17
32
56
44
8
14
29
30
32
30
1,000
1.750
59
Inhalation
exposure
(mg/day)*
17.500
3.172
462
798
"277
17,500
572
673
1.930
513
974
464
128
1.408
14,795
1.869
10.363
4,368
1.966
211
295
57
153
173
324
561
439
82
135
292
304
317
297
9,999
17,500
592
"Values are based on the geometric mean of the monitoring samples reported for a given job
Values are based on the assumption that the breathing rate for workers is 10 m /day
"Estimated number of workers based on average number of workers per plant multiplied by the
total number of plants identified.
The 'not classified' category represents data obtained from many types of industrial plants
which are not well defined.
Source: Adapted from 50FR42037. October 17. 1985.
-------
80 Section 7
7.5 POPULATIONS AT HIGH RISK
7.5.1 Above-Average Exposure
From the previous discussion, it is evident that a diverse number
of occupational subpopulations representing more than one million
workers are at risk for receiving DCM exposures substantially above the
general population.
Among the general population, transitory high-level atmospheric.
and sometimes dermal, exposures to DCM are commonly associated with the
use of DCM-containing paint strippers, adhesives, and aerosol products
for hobby and household uses. Further, the general widespread.
distribution of DCM throughout the atmosphere contributes additional
exposures to the general population that are usually classified as low
level, but may become significant in the vicinity of DCM industrial and
point-of-use areas (especially in urban areas).
Populations downstream from DCM production or use facilities may be
at increased risk of exposure from discharges into surface waters. Also,
populations near hazardous waste sites should be considered at high
exposure risk, especially if their drinking water supply Is derived from
local groundwater.
Certain products that contain DCM can expose consumers to
significant amounts of vapors and are thus hazardous. These have been
summarized in Sect. 7.4. The CPSC (1987) stated that it does not
currently have data showing that products in these categories that
contain 1% or less of DCM are hazardous substances.
7.5.2 Above-Average Sensitivity
Persons with compromised cardiovascular systems are considered to
be more sensitive to DCM exposure.
-------
81
8. ANALYTICAL METHODS
Gas chromatography (GC) is Che mosc common analytical method for
detecting and measuring DCH in environmental and biological samples.
Samples may be prepared by several methods, depending on the matrix
being sampled. The preparation procedures for analyzing environmental
samples for DCM include charcoal adsorption/desorption, purge and trap,
headspace sampling, and vacuum distillation (EPA 1983, 1986b; APHA 1977,
Page and Charbonneau 1977, 1984). Preparation of biological samples
often involves headspace sampling (DiVincenzo et al. 1971).
The GC separates complex mixtures of organics and allows individual
compounds to be identified and quantified.
Detectors used to identify DCH include a flame ionization detector
(FID), electron capture detector (ECD), and an electrolytic conductivity
detector and halogen-specific detector (HSD) (EPA 1983, 198Sa. 1986b;
APHA 1977; Page and Charbonneau 1984). When unequivocal identification
is required, a mass spectrometer (MS) coupled to a GC column (GC-MS) may
be used (EPA 1983, 1985d; Pellizzari and Bunch 1979).
Methylene chloride is a common laboratory contaminant and is
frequently found in laboratory blanks.
8.1 ENVIRONMENTAL MEDIA
Representative methods appropriate for measuring DCM in
environmental media are listed in Table 8.1.
8.1.1 Air
The American Public Health Association (APHA) method for measuring
of organic solvent vapors in air (834) is accepted by NIOSH
(Classification B) for application to DCM in workplace air. The method
involves adsorption of the organic vapors in the air onto an activated
charcoal filter, desorption with carbon disulfide, and injection of an
aliquot of the desorbed sample into a GC equipped with an FID. The
resulting peaks are measured and compared with standards (APHA 1977).
Interferences may be caused by high temperatures, high humidity,
high sampling flow rates, and other solvents with the same retention
times. Different GC column materials and temperatures may be used to
resolve the interference of other solvents (APHA 1977).
Other methods for measuring DCM in ambient air include GC/MS and
GC/ECD (EPA 1985d, Pellizzari 1974, Pellizzari and Bunch 1979).
-------
82 Section 8
Sample
matrix
Table 8.1. Analytical methods for methylene chloride in environmental samples
Sample
preparation
Analytical
method"
Sample
detection
limit
Accuracy*
References
Air Charcoal adsorption, GC/FIO
desorption with
carbon disulfide
Air Charcoal adsorption, GC/FID
desorption with
carbon disulfide
25 ppbc
90-110%' APHA 1977
10 mg/m3 95.3%
NIOSH 1984
Water
Soil
Food
Purge and trap
Purge and trap
Purge and trap
Purge and trap or
direct injection
Headspace sampling
Vacuum distillation
Vacuum distillation
GC/HSD
EPA method 601
GC/HSD
EPA method 624
GC/MS
EPA method 8010
GC/HSD
GC/ECD
GC/ECD
GC/EC
0.5 Mg/L«
0.25 Mg/L
2-8 Mg/L
ND^
0.05 ppm
7ng
7ng
104%
97.9%
96%
ND
ND
94%
100%
APHA 1985
EPA 1983
EPA 1983
EPA 1986b
Page and
Charbonneau 1984
Page and
Char-onneau 1977
Page and
Charbonneau 1977
"GC - gas chromatography; FID - name ionization detector, HSD = halogen-specific detector:
MS — mass spectrometry, BCD — electrolytic conductivity detector. EC - electron capture detector
* Average percent recovery.
'Lowest value for various detected compounds reported during collaborative testing.
'Estimated accuracy of the sampling and analytical method when the personal sampling pump is cali-
brated with a charcoal tube in the line.
'For most halogenated methanes and ethanes; not specific for DCM.
/Not determined.
-------
Analytical Methods 83
8.1.2 Water
The EPA approved two methods (601, 624) for analyzing wastevater
samples for DCM. These methods use a packed-column GC for separating
organic pollutants, but they differ in sample preparation procedures and
detection instrumentation.
Method 601 is optimized for purgeable halocarbons with a detection
limit of 0.25 A«g/L for DCM. Method 624, which employs MS for detection
and quantification, is broadly applicable to a large number of purgeable
organics and has a detection limit of 2.8 pg/L for DCM. The APHA
standard method for halogenated methanes and ethanes (514), like EPA
Method 601, uses purge-and-trap sample preparation and a halogen-
specific detector.
8.1.3 Soil
Soil samples can be analyzed for DCM by GC with a halogen-specific
detector. Sample preparation is by purge and trap. This method (8010) is
approved by the EPA for analysis of halogenated volatile organics in
solid waste. The method detection limit for DCM has not been determined
(EPA 1986b).
8.1.4 Food
Methylene chloride in food products (e.g., decaffeinated coffee,
spice, and oleoresins) may be measured by GC/ECD or GC with an
electrolytic conductivity detector (Page and Charbonneau 1984, 1977;
Page and Kennedy 1975). A GC/MS method may also be used for food
analysis (Hiatt 1981).
8.2 BIOMEDICAL SAMPLES
Methods appropriate for measuring DCM in biological samples are
listed in Table 8.2.
8.2.1 Fluids and Ezudates
Blood levels of DCM may be measured using GC with an FID. Headspace
sampling eliminates the need for an extraction procedure (DiVincenzo et
al. 1971). Infrared analysis has also been used for quantitative
estimation of volatile organics in blood, but the infrared method
requires an extraction step (DiVincenzo et al. 1971).
Analysis of urine for DCM is by the sane method used for blood.
Breath samples were also analyzed for DCM by GC/FID (DiVincenzo et al
1971).
8.2.2 Tissues
Human adipose tissue levels of DCM may be measured by GC/FID, using
hydrochloric acid to break down the adipose tissue and then a headspace
sampling method (Engstrom and Bjurstrom 1977).
-------
84 Section 8
Table 8.2. Analytical methods for methylene chloride in biological samples
Sample
Sample Sample Analytical detection
matrix preparation method" limit Accuracy References
Blood Headspace GC/FID 0.022 mg/L 49.8% DiVincenzo et al. 1971
sampling
Urine Headspace GC/FID ND* 59% DiVincenzo et al. 1971
sampling
Breath Gas sample GC/FID 0.2 ppm ND DiVincenzo et al. 1971
valve
Adipose Acid GC/FID 1.6 mg/kg* ND Engstrom and Bjurstrom
tissue hydrolysis 1977
headspace
sampling
"GC = gas chromatography; FID = flame iomzation detector.
*ND = not determined.
c Lowest reported concentration.
-------
85
9. REGULATORY AND ADVISORY STATUS
9.1 INTERNATIONAL
The World Health Organization (WHO) has not recommended a drinking
water guideline value for DCM.
9.2 NATIONAL
9.2.1 Regulations
Regulations applicable to DCM address occupational exposure
concentrations; reporting requirements; spill quantities; presence In
food, cosmetics, and hazardous waste; and tolerance requirements
exemptions (Table 9.1).
The Occupational Safety and Health Administration (OSHA) sets
Permissible Exposure Limits (PELs) for occupational exposures to
chemicals based on the recommendations of the NIOSH. The OSHA PELs for
DCM are 500 ppm (1,737 mg/m3) in workplace air for a time-weighted
average (TWA) (8 h/day, 40 h/week), a ceiling concentration of 1.000 ppm
(3,474 mg/m3), and a maximum peak, not to be exceeded for more than 5
min in 2 h, of 2,000 ppm (6,948 mg/m3) (OSHA 1986).
The EPA Office of Drinking Water (ODW) has promulgated monitoring
regulations for 51 unregulated volatile organic compounds (VOCs),
including DCM (52 FR 25690).
These regulations require the monitoring of public water supplies
in a program to be phased in over 4 years.
The Comprehensive Environmental Response, Compensation, and
Liability Act of 1980 (CERCLA) requires that persons in charge of
facilities from which a hazardous substance has been released in
quantities equal to or greater than its reportable quantity (RQ)
immediately notify the National Response Center of the release. The RQ
for DCM set by the EPA Office of Emergency and Remedial Response (OERR)
is 1,000 Ib.
Chemicals are included on the Resource Conservation and Recovery
Act (RCRA) Appendix VIII list of hazardous constituents (40 CFR Part
261) if they have toxic, carcinogenic, mutagenic, or teratogenic effects
on humans or other life forms. Methylene chloride is included on this
list, and wastes containing DCM are subject to the RCRA regulations
promulgated by the EPA Office of Solid Waste (OSW).
The Office of Toxic Substances (OTS) promulgates regulations
related to manufacturers and/or processors of chemicals that may present
an unreasonable risk to health or che environment. Manufacturers of DCM
are required to submit to EPA information on the quantity of the
-------
86
Section 9
Table 9.1. Regulations and guidelines applicable to methylene chloride
Agency
Description
Value
References
National Regulations
OSHA Permissible exposure limit (PEL) in
workplace air
Time-weighted average (TWA)
(8 h/day, 40 h/week)
Ceiling concentration
Maximum peak (not to exceed 5 min
in any 2 h)
EPA OERR Reportable quantity (RQ)
EPA OSW Hazardous constituent list
Appendix VIII
EPA OTS Preliminary assessment information rule
Health and safety data reporting rule
Comprehensive assessment information rule
(proposed)
FDA
Ban on use of methylene chloride in
cosmetics (proposed)
Limit in decaffeinated roasted coffee and
soluble coffee extract (instant coffee)
EPA OPP Exemption from tolerance
SOOppm
1,000 ppm
2,000 ppm
EPA ODW Monitoring regulations for unregulated VOCs NAa
1.000 Ib
NA
NA
NA
NA
NA
10 ppm
NA
29CFR
1910.1000
(1971)
40 CFR 141 40
52 FR 25690
(07/08/87)
40 CFR 302.4
40 CFR 1173
SOFR 13456
(04/04/85)
40 CFR 261
45 FR 33084
(05/19/80)
40 CFR 712
47 FR 26992
(06/22/82)
40 CFR 716
47 FR 38780
(09/02/82)
51 FR 35762
(10/07/86)
SOFR 51551
(12/18/85)
21 CFR
173.255
32 FR 12605
(08/31/67)
40 CFR
180.1010
36 FR 22540
(11/25/71)
-------
Regulacory and Advisory Status
87
Table 9.1 (condoned)
Agency
NIOSH
EPA ODW
NAS
IARC
EPA
ACGIH
Description
National Guidelines
Recommended exposure limit (REL)
Immediately dangerous to life or health
(IDLH)
Health advisories (HAs)
One-day (child)
Ten-day (child)
DWEL*
Suggested no adverse response level (SNARL)
One-day
Seven-day
Cancer ranking
Cancer ranking
Threshold limit value (TLV-TWA)
Value
Lowest
feasible
limit
5,000 ppm
13.3mg/L
1.5 mg/L
1.75 mg/L
45.5 mg/L
6.5 mg/L
Group 3
Group B2
50 ppm
(175mg/m3)
References
NIOSH 1986
NIOSH 1985
EPA 1985g
EPA 1985g
NAS 1980
IARC 1986
EPA 1985g
ACGIH 1986
"NA = not available.
* DWEL =* drinking water equivalent level.
-------
88 Section 9
chemical manufactured or imported, the amount directed to certain uses,
and the potential exposure and environmental release of the chemical
under the Preliminary Assessment Information Rule. Unpublished health
and safety studies on DCH must be submitted to EPA by manufacturers or
processors under the Health and Safety Data Reporting Rule. The OTS has
proposed a Comprehensive Assessment Information Rule (CAIR) that would
specify the reporting requirements for chemicals for which EPA requires
information. This rule is designed to streamline the collection of
information to support chemical risk assessment/management strategies.
Methylene chloride is one of the 47 chemicals proposed to be included in
this rule.
The OTS has initiated a priority review for risks of human cancer
from certain exposures to DCH and will conduct a regulatory
investigation of the chemical in consultation with other federal
agencies (50 FR 42037).
The Food and Drug Administration (FDA) regulates the use of
chemicals in foods, drugs, and cosmetics. The FDA proposed a ban on the
use of DCM as an ingredient in aerosol cosmetic products (primarily hair
sprays), based on recent studies which have shown that inhalation of DCM
causes cancer in laboratory animals. The FDA maximum permitted residue
level of DCM in decaffeinated coffee is 10 ppm. Other FDA regulations
applicable to DCM include its use in hops extraction, adhesives,
polycarbonate resins, and dilutents in color additive mixtures [as
related to food (50 FR 51551)].
The EPA Office of Pesticide Products (OPP) has exempted DCM from
the requirement of a tolerance for residues when used as a fumigant
after harvest for several grains and citrus fruits.
9.2.2 Advisory Guidance
Advisory guidance levels are environmental concentrations
recommended by either regulatory agencies or other organizations that
are protective of human health or aquatic life. While not enforceable,
these levels may be used as the basis for enforceable standards.
Advisory guidance for DCM is summarized in Table 9.1 and includes the
following: occupational exposure levels, ambient water quality criteria,
health advisory levels for drinking water, and suggested-no-adverse-
response levels (SNARLs) calculated by the National Academy of Sciences
(NAS).
The American Conference of Governmental Industrial Hygienists
(ACGIH) recently proposed a provisional recommendation to reduce the
threshold limit value (TLV) TWA for DCM from 100 to 50 ppm and to
eliminate the short-term exposure limit (STEL) in order to provide a
wider margin of safety in preventing liver injury. This level should
also provide protection against the possible weak carcinogenic effect of
DCM that has been demonstrated in laboratory rats and mice.
The NIOSH recently changed the Recommended Exposure Limit (REL) for
DCM from a TWA of 75 ppm to the lowest feasible limit, based on the
assessment of DCM as a potential occupational carcinogen. The NIOSH
Immediately Dangerous to Life or Health (IDLH) level for DCM is
-------
Regulatory and Advisory Scacus 89
5,000 ppm. This level represents a maximum concentration from which one
could escape within 30 min without any escape- impairing symptoms or
irreversible health effects.
The ODW prepared health advisories (HAs) for numerous drinking
water contaminants. The HAs describe concentrations of contaminants in
drinking water at which noncarcinogenic effects would not be anticipated
to occur and would include a margin of safety to protect sensitive
members of the population. The HAs are calculated for One-day, Ten-day,
Longer-term, and Lifetime exposures. The One-day HA and Ten-day HA are
calculated for exposure of children; for DCM, these values are 13.3 and
1.5 mg/L, respectively. Adequate data for calculating a Longer-term HA
were not available. Methylene chloride has been classified by EPA as a
B2 carcinogen; therefore, a lifetime HA value is not recommended.
However, a DUEL of 1.75 mg/L has been recommended.
The NAS calculated One -day and Seven -day SNARLs for DCM. The NAS
(1980) listed the One-day SNARL as 35 mg/L and the Seven-day SNARL as
5 mg/L. Subsequent evaluation of these data indicated that values should
be 45.5 mg/L and 6.5 mg/L, respectively (EPA 1985g) . Because of the lack
of suitable data, a chronic SNARL was not calculated.
9.2.3 Data Analysis
9.2.3.1 Reference doses
A reference dose (RfD) has been calculated for DCM. It was based on
a 2-year rat study by NCA (1982). In this study, four groups of animals
(85 rats/sex/group) were given DCM in drinking water at target doses of
0, 5, 50, 125, and 250 mg/kg/day. Hepatic histological alterations that
were detected in the 50- to 250-mg/kg/day dose groups (both sexes)
included an increased incidence of foci and areas of cellular
alteration. Fatty liver changes were detected in the 125- and
250-mg/kg/day groups at 78 and 104 weeks of treatment. An RfD can be
determined using the following general formula:
RfD - ' the **" ls the modifying factor .
Based on findings of the 2-year rat study, an RfD was calculated (not
requiring the use of a modifying factor) as follows:
where
RfD _ (5 -y-*r—ri . o.05 mgAg/day (100) ,
5 mg/kg/day - NOAEL
100 - uncertainty factor appropriate for use with NOAEL
from animal study.
-------
90 Section 9
9.2.3.2 Carcinogenic potency
In evaluating the potential carcinogenicity of DCM, the EPA
Carcinogen Assessment Group (GAG) calculated a human potency estimate by
fitting liver and lung tumor data from female B6C3F1 mice in the NTP
inhalation study with the linearized multistage model and performing an
interspecies extrapolation to humans based on a surface area correction
(EPA L985b). The potency factor, q.*, which represents a 95% upper
confidence limit of the extra lifetime human risk, is 1.4 x 10'*
(mg/kg/day)*^. The unit risk estimate for inhalation exposures is
4.1 x 10'6 (/ig/m3)'1.
The EPA (1987a,b) is considering lowering its previous risk
estimate (EPA 198Sb) to 4.7 x 10*7 (^/n3)'1 on the basis of
pharmacokinetics data reported by Andersen et al (1987). In the risk
assessment published in 1985 (EPA 1985b), exposure levels corresponding
to excess lifetime human cancer risks of 10'*, 10'5, and 10'6 are 200,
20, and 2 pg/m3 (0.057, 0.0057, and 0.00057 ppm), respectively. The
revision based on pharmacokinetics data would raise these exposures by
about an order of magnitude.
Both risk assessments (EPA 1985b, 1987a,b) are based on the
linearized multistage model. Risk estimates made with this model should
be regarded as conservative, representing a plausible upper limit for
the risk. The true risk is not likely to be higher than the estimate,
but it may be lower. To provide a comparison with the linearized
multistage model risk estimate, CAG (EPA, 1985b) applied the probit,
Ueibull, and time-to-tumor models to the mouse data. The time-to-tumor
model estimated risks that were similar to those estimated by the
linearized multistage model. For combined lung and liver tumors in
female mice, the background-additive implementation of both the probit
and Veibull models were in good agreement with the multistage model.
However, the background-independent implementations of the probit and
Veibull models lead to much lower risk estimates.
9.3 STATE
(Regulations and advisory guidance from the states were still being
compiled at the time of printing.)
9.3.1 Regulations
Methylene chloride is not specified in any state water quality
standards. However, this compound is included in the category "toxic
substances" in the water quality standards of most states in narrative
form. Specific narrative standards protect the use of surface waters for
public water supply and contact recreation.
9.3.2 Advisory Guidance
No information on state advisory guidance was available.
-------
91
10. REFERENCES
ACGIH (American Conference of Government Industrial Hygienists). 1986.
Documentation of the Threshold Limit Values and Biological Exposure
Indices. 5th ed. Cincinnati, OH.
Altshuller AP. 1980. Lifetimes of organic molecules in the troposphere
and lower stratosphere. Adv Environ Sci Technol 10:181-219.
Anders MW, Kubic VL, Ahmed AE. 1977. Metabolism of halogenated methanes
and macromolecular binding. J Environ Pathol Toxicol 1:117-124.
Anders MW, Sunram JM. 1982. Transplacental passage of dichloromethane
and carbon monoxide. Toxicol Lett 12(4):231-234.
Andersen ME, Clewell HJ, Gargas ML, Smith FA, Reitz RH. 1987.
Physiologically based pharmacokinetics and the risk assessment process
for methylene chloride. Toxicol Appl Pharmacol 87:185-205.
Andrae U, Wolff T. 1983. Oichloromethane is not genotoxic in isolated
rat hepatocites. Arch Toxicol 52:287-290.
Angelo MJ, Pritchard AB. 1984. Simulations of methylene chloride
pharmacokinetics using a physiologically based model. Reg Toxicol
Pharmacol 4:329-339.
* Angelo MJ, Pritchard AB, Hawkins OR, Waller AR, Roberts A. 1986a. The
pharmacokinetics of dichloromethane. II. Disposition in Fischer 344 rats
following intravenous and oral administration. Food Chem Toxicol
24(9):975-980.
* Angelo MJ, Pritchard AB, Hawkins DR, Waller AR, Roberts A. 1986b. The
pharmacokinetics of dichloromethane. I. Disposition in B6C3F1 mice
following intravenous and oral administration. Food Chem Toxicol
24(9):965-974.
APHA (American Public Health Association). 1977. Methods of Air Sampling
and Analysis. 2nd ed. Washington, DC: American Public Health
Association, pp. 894-902.
Key studies.
-------
92 Section 10
APHA (American Public Health Association). 1985. Standard Methods for
the Examination of Water and Wastewater. 16th ed. Washington, DC:
American Public Health Association.
Astrand I, Ovrum P, Carlsson A. 1975. Exposure to methylene chloride. I.
Its concentration in alveolar air and blood during rest and exercise and
its metabolism. Scand J Work Environ Health 1:78-94.
Aviado DM, Belej MA. 1974. Toxicity of aerosol propellants on the
respiratory and circulatory systems. I. Cardiac arrythmia in the mouse.
Toxicology 2:31-42.
Aviado DM, Zakhari S, Watanabe T. 1977. Methylene chloride. In: Goldberg
L, ed. Non-Fluorinated Propellants and Solvents for Aerosols, Cleveland,
OH: CRC Press, pp. 19-45.
Ballantyne B, Guzzard MF, Swanson DW. 1976. Ophthalmic toxicology of
dichloromethane. Toxicology 6:173-187
Balmer FM, Smith FA, Leach LJ, Yuile, CL. 1976. Effects in the liver of
methylene chloride inhaled along and with ethyl alcohol. Am Ind Hyg
Assoc J 37:345-352.
Barnes D et al. 1987. Reference dose (RfD): Description and use in
health risk assessments. Appendix A in Integrated Risk Information
System Supportive Documentation. Vol. 1. Office of Health and
Environmental Assessment, Environmental Protection Agency, Washington,
DC. EPA/600/8-86/032a.,
Bellar TA, Lichtenberg JJ, Kroner RC. 1974. The occurrence of
organohalides in chlorinated drinking waters. J Am Water Works Assoc
703-706.
Berger M, Fodor GG. 1968. CNA disorders under the influence of air
mixtures containing dichloromethane. Zentrabl Bakteriol 215:417.
Bonventre J, Brennan D, Juson D, Henderson A, Bustos ML. 1977. Two
deaths following accidental inhalation of dichloromethane and
1,1,1-trichloroethane. J Anal Toxicol 1:158-160.
Bornmann G, Loeser A. 1967. Zur Frage einer Chronisch - toxischen
Wirkung von dichloromethan. z. Lebensm-unters. Forsch 136:14-18 (cited
in EPA 1985c).
Brodzinaki R, Singh HB. 1983. Volatile Organic Chemicals in the
Atmosphere: An Assessment of Available Data. Environmental Protection
Agency. EPA-600/S 3-83-027.
Brunner WD, Staub D, Leisinger T. 1980. Bacterial degradation of
dichloromethane. Appl Environ Microbiol 40:950-958.
-------
References 93
Burek JD, Nitschke KD, Bell TJ, et al. 1980. Methylene Chloride: A
Two-Year Inhalation Toxiclty and Oncogenicity Study in Rats and
Hamsters. Toxicology Research Laboratory, Health and Environmental
Sciences, Dow Chemical Company, Midland, MI.
Burek JD, Nitschke KD, Bell TJ, et al. 1984. Methylene chloride: A
two-year inhalation toxicity and oncogenicity study in rats and
hamsters. Fundam Appl Toxicol 4(1):30-47.
Butler R. Solomon IJ, Snelson A. 1978. Rate constants for the reaction
of OH with halocarbons in the presence of 02 + N2. J Air Pollut Control
Assoc 28:1131-1133.
Carlsson A, Hultengrene M. 1975. Exposure to methylene chloride. III.
Metabolism of 14C-labelled methylene chloride in rat. Scand J Work
Environ Health 1:104-108.
* CEFIC (European Center of Chemical Manufacturer's Federation). 1986a
In: Green T, Nash JA, Mainwaring G, eds. Methylene Chloride: In Vitro
Metabolism in Rat, Mouse, and Hamster Liver and Lung Fractions and in
Human Liver Fractions. ICI Central Toxicology Laboratory, Report
CTL/R/879, September 22.
CEFIC (European Center of Chemical Manufacturer's Federation). 1986b.
In: Green T, Provan WM, Collinge DC, Guest AE, eds. Methylene Chloride
Interaction with the Rat and Mouse Liver and Lung DNA In Vivo. ICI
Central Toxicology Laboratory, Report CTL/R/851, January 22.
CEFIC (European Center of Chemical Manufacturer's Federation). 1986c.
In: Truman RW, Ashby J, eds. Methylene Chloride: In Vivo and In Vitro
Unscheduled DNA Synthesis Studies in the Mouse and the Rat. ICI Central
Toxicology Laboratory, Report CTL/P 1444, January 21.
* CEFIC (European Center of Chemical Manufacturer's Federation). 1986d
In: Lefevre PA, Ashby J, eds. Methylene Chloride: Induction of S-Phase
Hepatocytes in the Mouse After In Vivo Exposure. ICI Central Toxicology
Laboratory, Report CTL/R/885, September 22.
CEFIC (European Center of Chemical Manufacturer's Federation). 1986e
In: Sheldon T, Richardson CR, Hamilton K, Randell V, Hart D, Hollis K,
eds. Methylene Chloride: An Evaluation in the Mouse Micronucleus Test.
ICI Central Toxicology Laboratory, Report CTL/P/1603, September 19.
Cherry N, Venable H, Waldron H. 1983. The acute behavioral effects of
solvent exposure. J Soc Occup Med 33:13-18.
Clevell HJ, Andersen ME. 1985. Risk assessment extrapolations and
physiological modeling. Toxicol Ind Health 1:111-131.
-------
94 Section 10
Coleman WE, Llngg RD, Melton RG, Kopfler FC. 1976. The occurrence of
volatile organics in five drinking water supplies using gas
chromatography/mass spectrometry. Chap. 21. In: Keith LH, ed.
Identification and Analysis of Organic Pollutants in Water. Ann Arbor,
HI: Ann Arbor Science.
Cox RA, Denwent RC, Eggleton AEJ, Lovelock JE. 1976. Photochemical
oxidation of halocarbons in the troposphere. Atmos Environ 10:305-308.
CPSC (Consumer Product Safety Commission). 1987. Labeling of certain
household products containing methylene chloride; statement of
interpretation and enforcement policy. Fed Regist 52(7):34698.
Cronn DR. Robinson E. 1979. Determination of trace- gases in Learjet and
U-2 whole-air samples collected during the intertropical convergence
zone study. In: Poppoff IG, Page WA, Margozzi AP, eds. 1977
Intertropical Convergence Zone Experiment. NASA TMX78577.
Cronn DR, Rasmussen RA, Robinson E. 1977. Report for Phase II.
Measurement of Tropospheric Halocarbons by Gas Chromatography/Mass
Spectrometry. Prepared for the Environmental Protection Agency.
Crutzen PJ, Fishman J. 1977. Average concentrations of OH- in the
troposphere and the budgets of CH4, CO, H2, and CH3CC13. Geophys Res
Lett 4:321-324.
Davis DD, Machado G, Conaway B, Oh Y, Watson R. 1976. A temperature-
dependent kinetics study of the reaction of OH with CH3C1, CH2C12,
CHC13, and CH3. Br J Chem Phys 65(4):1268-1274.
Davis EM et al. 1981. Water Res 15:1125-1127.
Dewalle FB, Chian ESK. 1978. Proc Ind Waste Conf 32:908-919.
Dilling WL, Tefertiller NB, Kallos GJ. 1975. Evaporation rates of
methylene chloride, chloroform, 1,1,1-trichloroethane,
trichloroethylene, tetrachloroethylene, and other chlorinated compounds
in dilute aqueous solutions. Environ Sci Techno1 9(9):833-838.
DiVincenzo CD, Yanno FJ, Astill BD. 1971. The gas chromatographic
analysis of methylene chloride in breath, blood, and urine. Am Indus Hyg
Assoc J 32:387-391.
DiVincenzo CD, Yanno FJ, Astill BD. 1972. Human and canine exposure to
methylene chloride vapor. Am Ind Hyg Assoc J 33:125-135.
DiVincenzo GD, Kaplan CJ. 1981. Uptake, metabolism, and elimination of
methylene chloride vapor by humans. Toxicol Appl Pharmacol 59:130-140
Dowty BJ, Carlisle DR, Laseter JL. 1975. New Orleans drinking water
sources tested by gas chromatography/mass spectrometry. Environ Sci
Technol 9(8):762-765.
-------
References 95
Dyksen JE, Hess AF III. 1982. J Am Water Works Assoc 1982:394-403.
Elovaara E, Hemminki K, Vainio H. 1979. Effects of methylene chloride.
trichloroethane, trichloroethylene, tetrachloroethylene, and toluene on
the development of chick embryos. Toxicology 12:111-119.
Engstrom J, Bjurstrom R. 1977. Exposure to methylene chloride: Content
in subcutaneous adipose tissue. Scand J Work Environ Health 3:215-224.
EPA (Environmental Protection Agency). 1975a. Preliminary Assessment of
Suspected Carcinogens in Drinking Water. Report to Congress. EPA-
560/14-75-005. PB 260961.
EPA (Environmental Protection Agency). 1975b. Region V Joint
Federal/State Survey of Organics and Inorganics in Selected Drinking
Water Supplies.
EPA (Environmental Protection Agency). 1980. Ambient Water Quality
Criteria for Halomethanes. Environmental Criteria and Assessment Office,
Office of Water Regulations and Standards, Washington, DC.
EPA-440/5-80.
EPA (Environmental Protection Agency). 1981a. Treatability Manual.
EPA-600/2-82-001A, pp. 1.12.2-1 - 1.12.2-4.
EPA (Environmental Protection Agency). 1981b. Environmental Risk
Assessment of Dichloromethane. Draft report. Office of Toxic Substances.
EPA (Environmental Protection Agency). 1983. Methods for Chemical
Analysis of Water and Wastes. Office of Research and Development,
Environmental Monitoring and Support Laboratory, Cincinnati, OH.
EPA-600/4-79-020.
EPA (Environmental Protection Agency). 1985a. Health Assessment Document
for Dichloromethane. Final report. Office of Health and Environmental
Assessment, Washington, DC. EPA/600/8-82/004F.
EPA (Environmental Protection Agency). 1985b. Addendum to the Health
Assessment Document for Dichloromethane (Methylene Chloride). Updated
Carcinogen Assessment of Dichloromethane (Methylene Chloride). Final
draft. Office of Research and Development, Washington, DC. EPA 600/8-
82-0044FF.
EPA (Environmental Protection Agency). 1985c. Criteria Document on
Dichloromethane. Final draft. Office of Drinking Water, Washington, DC.
EPA (Environmental Protection Agency). 1985d. Health Effects Assessment
for Methylene Chloride. Office of Health and Environmental Assessment,
Washington, DC. Cincinnati, OH: Office of Emergency and Remedial
Response.
-------
96 Section 10
EPA (Environmental Protection Agency). 1985e. Environmental Profiles and
Hazard Indices for Constituents of Municipal Sludge: Methylene Chloride.
Office of Water Regulations and Standards, Criteria and Standards
Division.
EPA (Environmental Protection Agency). 1985f. Summary of Environmental
Profiles and Hazard Indices for Constituents of Municipal Sludge:
Methods and Results. Office of Water Regulations and Standards, Criteria
and Standards Division.
EPA (Environmental Protection Agency). 1985g. Health Advisory for
Dichloromethane. Draft. Office of Drinking Water, Washington, DC.
EPA (Environmental Protection Agency). 1985h. Analysis of the
Applicability of TSCA Section 4(f) to Methylene Chloride. Prepared by
J. Hopkins.
EPA (Environmental Protection Agency). 1986a. Superfund Public Health
Evaluation Manual. Office of Emergency and Remedial Response,
Washington, DC. EPA 540/1-86-060.
EPA (Environmental Protection Agency). 1986b. Test Methods for
Evaluating Solid Waste. 3rd ed. Office of Solid Waste and Emergency
Response, Washington, DC. SW-846.
EPA (Environmental Protection Agency). 1986c. Guidelines for carcinogen
risk assessment. Fed Regist 51(195):33992-34003.
* EPA (Environmental Protection Agency). 1987a. Technical Analysis of
New Methods and Data Regarding Dlchloromethane Hazard Assessments. Draft
document.
* EPA (Environmental Protection Agency). 1987b. Update to Health
Assessment Document and Addendum for Dichloromethane (Methylene
Chloride): Pharmacokinetics, Mechanism of Action, and Epidemiology.
Draft report. EPA 600/8-87/1030A.
Ewing BB, Chi an ESK. Cook JC, Evans CA, Hopke PK, Perkins EG. 1977.
Monitoring to Detect Previously Unrecognized Pollutants in Surface
Waters. Environmental Protection Agency. EPA-560/6-77-015.
Flury Fanil Zernik F. 1931. Harmful Gases, Vapors, Fog, Smoke, and Dust.
Berlin: Julius Springer, pp. 311-312.
Fodor GG, Winneke G. 1971. Nervous system disturbances in men and
animals experimentally exposed to industrial solvent vapors in England.
Proceedings of the 2nd International Clean Air Congress. New York:
Academic Press.
Fodor GG, Prajsnar D, Schlipkoter HW. 1973. Endogenous cofornation by
incorporated halogenated hydrocarbons of the methane series.
Staubreinhalt Luft 33:260-261.
-------
References 97
Fodor GG, Roscovana G. 1976. Increased blood-CO content in humans and
animals by incorporated halogenated hydrocarbons. Zentrabl Bukteriol
(Orig B) 162:34 (German) (cited in EPA 1985a).
Forster HV, Graff S, Hake CL, Soto R, Stewart RD. 1974. Pulmonary-
Hematologic Studies on Humans During Exposure to Methylene Chloride.
NIOSH-MCOW-ENVM-MC-74-4.
Friedlander BR, Hearne FT. Hall S. 1978. Epidemiologic investigation of
employees chronically exposed to methylene chloride--mortality analysis
J Occup Hed 20(10):657-666.
Gargas ML, Clewell HJ, Andersen ME. 1986. Metabolism of inhaled
dihalomethanes in vivo: Differentiation of kinetic constants for two
independent pathways. Toxicol Appl Pharmacol 82:211-223.
Gocke E, King M-T, Eckhardt K, Wild D. 1981. Mutagenicity of cosmetic
ingredients licensed by European Communities. Mutat Res 90:91-109.
Gradiski D, Bonnet G, Raoult G, Magadur JL. 1978. Compared acute
pulmonary toxicity of the main chlorinated aliphatic solvents (French).
Arch Mai Prof Med Trav Secus Soc 39:249.
Grimsrud EP, Rasmussen RA. 1975. Survey and analysis of halocarbons in
the atmosphere by gas chromatography-mass spectrometry. Atmos Environ
9:1014-1017.
Hardin BD, Manson JM. 1980. Absence of dichloromethane teratogenicity
with inhalation exposure to rats. Toxicol Appl Pharmacol 52(1):22.
Harkov R, Giante SJ Jr., Bozelli JW, LaRegina JE. 1985. Monitoring
volatile organic compounds at hazardous and sanitary landfills in New
Jersey. J Environ Sci Health A20(5):491-501.
* Haun CC, Vernot EH, Darmer KI, Diamond SS. 1972. Continuous animal
exposure to low levels of dichloromethane. In: Proceedings of the Third
Annual Conference on Environmental Toxicology. Wright-Patterson Air
Force Base, OH: Aerospace Medical Research Laboratory. AMRL-TR-72-130,
pp. 199-208.
Hearne FT, Grose F, Pifer JW. Friedlander BR, Raleigh RL. 1987.
Methylene chloride mortality study: Dose-response characterization and
animal model comparison. J Occup Med 29:217-228.
Helz GR, Hus RY. 1978. Limnol Oceanogr 23:858-869.
Heppel LA, Neal PA. 1944. Toxicology to dichloromethane (methylene
chloride). II. Its effects upon running activity in the male rat. J
Indust Hyg Toxicol 26:17-21.
Heppel LA, Neal PA, Perrin ML, On VT. 1944. Toxicology of
dichloromethane (methylene chloride). I. Studies on effects of daily
inhalation. J Indust Hyg Toxicol 26 8-16.
-------
98 Section 10
Hlatt MH. 1981. Analysis of fish and sediment for volatile priority
pollutants. Anal Chem 53:1541-1543.
HSDB (Hazardous Substances Data Bank). 1987. Record for dichloromethane
Computer printout. National Library of Medicine, April 9, 1987.
HSIA (Halogenated Solvents Industry Alliance). 1988. Public comments on
scientific and technical issues on the Draft Toxicological Profile for
Methylene Chloride. Submitted to Agency for Toxic Substances and Disease
Registry (ATSDR) March 8.
IARC (International Agency for Research on Cancer). 1986. Some
halogenated hydrocarbons and pesticide exposures. IARC Monograph on the
Evaluation of the Carcinogenic Risk of Chemicals to Humans. 41:43-85.
ICAIR. 1985. Chemical Profile: Methylene Chloride. ICAIR Life Systems
Cleveland, OH. TR-894-30.
Illing HPA, Shillaker RO. 1985. Toxicity Review 12. Dichloromethane
(Methylene Chloride). Health and Safety Executive. Her Majesty's
Stationary Office, London, England.
Jongen WMF, Lehman PHM, Kottenhagen MJ, Alink GM, Berends F. Koeman JH.
1981. Mutagenicity testing of dichloromethane in short-term mammalian
test systems. Mutat Res 81:203-213.
Kimura ET, Ebert DM, Dodge PW. 1971. Acute toxicity and limits of
solvent residue for sixteen organic solvents. Toxicol Appl Pharmacol
19:699-704.
Klecka GM. 1982. Fate and effects of methylene chloride in activated
sludge. Appl Environ Microbiol 44:701-707.
Konasewich D et al. 1978. Status Report on Organic and Heavy Metal
Contaminants in the Lakes Erie, Michigan, Huron, and Superior Basins.
Great Lake Water Quality Board, p. 373.
Kuzelova MR, Vlasak. 1966. The effect of methylene dichloride on the
health of workers in production of film foils and investigation of
formic acid as the methylene dichloride metabolite (Czech). Pracov Lek
18:167-170 (cited in NIOSH 1976).
LaPat-Polasko LT, McCarty PL, Zehnder AJB. 1984. Secondary substrate
utilization of methylene chloride by an isolated strain of Pseudononas
Appl Environ Microbiol 47(4):825-830.
Latham S, Potvln M. 1976. Microdetermination of dichloromethane in blood
with a syringeless gas chromatographic injection system. Chemosphere
6:403-411.
MacEwen JD, Vernot EH, Haun CC. 1972. Continuous Animal Exposure to
Dichloromethane. Wright-Patterson Air Force Base, OH: Aerospace Medical
Research Laboratory. AMRL-TR-72-28.
-------
References 99
Maksimov GG, Mamleeva NK, Malyarova LK. 1977. Distribution,
accumulation, and excretion of methylene chloride following its entry
through the skin (Russian) . Kozhn Put Postupleniya Prom Yadov v
Organizm. i Ego Prof ila-ktika: 17-21 (cited in EPA 1985c) .
McCarroll NE, Cortina TA, Zieo HJ , Farrow MG. 1983. Evaluation of
methylene chloride and vinylidene chloride in mutational assays. Environ
Mutagenesis 5:426-427.
McConnell FE, Solleveld HA, Swenberg JA, Boorman GA. 1986. Guidelines
for combining neoplasms for evaluation of rodent carcinogenesis studies.
J Natl Cancer Inst 76:283-289.
McDougal JN, Jepson GV, Clewell HJ , MacNaughton MG, Andersen ME. 1986. A
physiological pharmacokinetic model for dermal absorption of vapors in
the rat. Toxicol Appl Pharmacol 85:286-294.
McKenna MJ, Saunders JH, Boeckler WH, Karbowski RJ , Nitschke KD,
Chenoweth MB. 1980. The pharmacokinetics of inhaled methylene chloride
in human volunteers. Toxicol Appl Pharmacol A59 (abstract).
* McKenna MJ, Zempel JA. 1981. The dose -dependent metabolism of
methylene chloride following oral administration to rat. Food Cosmet
Toxicol 19:73-78.
* McKenna MJ, Zempel JA, Braun WH. 1982. The pharmacokinetics of inhaled
methylene chloride in rats. Toxicol Appl Pharmacol 65:1-10.
Moody DE. 1981. Correlations among changes in hepatic microsomal
components after intoxication with alkyl halides and other hepatotoxins .
Mol Pharmacol 20:685-693.
Morris JB, Smith FA, Carman RH. 1979. Studies on methylene chloride-
induced fatty liver. Exp Mol Pathol 30:386-393.
NAS (National Academy of Sciences). 1977. Drinking Water and Health.
Washington, DC: National Academy Press, pp. 743-745.
NAS (National Academy of Sciences). 1978. Non- Fluor ina ted Halomethanes
in the Environment. Panel on Low-Molecular-Weight Halogenated
Hydrocarbons. Coordinating Committee for Scientific and Technical
Assessments of Environmental Pollutants.
NAS (National Academy of Sciences). 1980. Drinking Water and Health.
Vol. 3. Washington, DC: National Academy Press.
* NCA [National Coffee Association (prepared by Hazelton Laboratories
American, Inc.)]. 1983. 24-Month Oncogenicity Study of Methylene
Chloride in Mice. Vienna, VA: Unpublished (reported in Serota et al.
1984) .
-------
100 Section 10
* NCA [National Coffee Association (prepared by Hazelton Laboratories
American, Inc.)]. 1982. 24-Month Chronic Toxicity and Oncogenicity Study
of Methylene Chloride in Rats. Final report. Vols. I-IV. Vienna, VA:
Unpublished. 2112-101.
NFPA (National Fire Protection Association). 1978. Fire Protection Guide
for Hazardous Materials.
NIOSH (National Institute for Occupational Safety and Health). 1976.
Criteria for a Recommended Standard...Occupational Exposure to Methylene
Chloride. Cincinnati. OH. U.S. DHEW Publ. 76-138.
NIOSH (National Institute for Occupational Safety and Health). 1984.
NIOSH Manual of Analytical Methods. Vol. 2. 3rd ed. Cincinnati, OH:
Department of Health and Human Services.
NIOSH (National Institute for Occupational Safety and Health). 198S.
NIOSH Pocket Guide to Chemical Hazards. Washington, DC: Department of
Health and Human Services.
NIOSH (National Institute for Occupational Safety and Health). 1986.
Current Intelligence Bulletin 46 - Methylene Chloride. Cincinnati, OH:
Department of Health and Human Services.
Nitschke KD, Burek JD, Bell TJ, Kociba RJ, Rampy LW, McKenna MJ. 1988.
Methylene chloride: A 2-year inhalation toxicity and oncogenicity study
in rats. Fundam Appl Toxicol 11:48-59.
* Nitschke K, Eisenbrandt DL, Lomax LC. 1985. Methylene chloride: Two-
generation inhalation reproduction study in Fischer 344 rat. Halogenated
Solvents Industry Alliance, Unpublished (currently being peer reviewed,
October/November 1987).
Nitschke KD, Eisenbrandt DL, Lomax LG, Rao KS. 1988. Methylene chloride.
Two-generation inhalation reproductive study in rats. Fundam Appl
Toxicol 11:60-67.
* Nitschke KD, Burek JD, Bell TJ, Rampy LW. McKenna MG. 1982. Methylene
Chloride: A Two-Year Inhalation Toxicity and Oncogenicity Study.
Toxicology Research Laboratory, Health and Environmental Sciences, Dow
Chemical. Final report.
Norpoth K, Witting U, Springoram M, Wittig C. 1974. Induction of
microsomal enzymes in the rat liver by inhalation of hydrocarbon
solvents. InC Arch Arbeitmed 33(4):315-321 (cited in EPA 1985).
* NTP (National Toxicology Program). 1986. Toxicology and Carcinogenesis
Studies of Dichloromethane (Methylene Chloride) (CAS 75-09-2) in F344/N
Rats and B6C3F1 Mice (Inhalation Studies). Tech Rep Ser 306.
ORVWSC (Ohio River Valley Water Sanitary Commission). 1982. Assessment
of Wa«:er Quality Conditions. Ohio River Mainstream. 1981-1982. Table 13
-------
References 101
OSHA (Occupational Safety and Health Administration). 1979. General
Industry Standards. (OSHA) 2206, Revised January 1978. Department of
Labor, Washington, DC.
OSHA (Occupational Safety and Health Administration). 1986. Occupational
exposure to methylene chloride. Fed Regist 51:42257.
Ott MG, Skory LK, Holder BB. Bronson JM, Williams PR. 1983a. Health
evaluation of employees occupationally exposed to methylene chloride -
mortality. Scand J Work Environ Health 9(Suppl 1):8-16.
Ott MG, Skory LK, Holder BB, Bronson JM, William PR. 1983b. .Health
evaluation of employees occupationally exposed to methylene chloride
Twenty-four hour electrocardiographic monitoring. Scand J Work Environ
Health 9:26-30.
* Ott MG, Skory LK, Holder BB, Bronson JM, William PR. 1983c. Health
evaluation of employees occupationally exposed to methylene chloride.
Metabolism data and oxygen half saturation pressure. Scand J Work
Environ Health 9:31-38.
Page BD, Charbonneau CF. 1977. Gas chromatographic determination of
residual methylene chloride and trichloroethylene in decaffeinated
instant and ground coffee with electrolytic conductivity and electron
capture detection. J Assoc Off Anal Chem 60:710-715.
Page BD, Charbonneau CF. 1984. Headspace gas chromatographic
determination of methylene chloride in decaffeinated tea and coffee,
with electrolytic detection. J Assoc Off Anal Chem 67:757-761.
Page BD, Kennedy BPC. 1975. Determination of methylene chloride.
ethylene dichloride, and trichloroethylene as solvent residues in spice
oleoresins, using vacuum distillation and electron capture gas
chromatography. J Assoc Off Anal Chem 58:1062-1068.
Pearson CR, McConnell G. 1975. Chlorinated Cl and C2 hydrocarbons in the
marine environment. Proc R Soc London B 189:305-332.
Pellizzari ED. 1974. Electron capture detection in gas chromatography. J
Chromatogr 98:323-361.
Pellizzari ED. 1977. Analysis of Organic Air Pollutants by Gas
Chromatography and Mass Spectroscopy. Environmental Protection Agency
EPA-600/2-77-100.
Pellizzari ED. 1978a. Measurement of Carcinogenic Vapors in Ambient
Atmospheres. Environmental Protection Agency. EPA-600/7-78-062.
Pellizzari ED. 1978b. Quantification of Chlorinated Hydrocarbons in
Previously Collected Air Samples. Environmental Protection Agency.
EPA-450/3-78-112.
-------
102 Section 10
Pellizzari ED, Bunch JE. 1979. Ambient Air Carcinogenic Vapors: Improved
Sampling and Analytical Techniques and Field Studies. Environmental
Protection Agency. EPA-600/2-79-081.
Pellizzari ED, Erickson MD, Zweidinger RA. 1979. Formulation of a
Preliminary Assessment of Halogenated Organic Compounds in Man and
Environmental Media. Environmental Protection Agency. EPA-560/13-179-006
Perocco P, Prodi G. 1981. DNA damage by halokanes in human lymphocytes
cultured in vitro. Cancer Lett 13:213-218.
Peterson JE. 1978. Modeling the uptake, metabolism, and excretion of
dichloromethane by man. Am Ind Hyg Assoc J 39:41-47.
Ramsey JC, Andersen ME. 1984. A physiologically based description of the
inhalation pharmacoklnetics of styrene in rats and humans. Toxicol Appl
Pharmacol 73:159-175.
Ramussen RA, Harsch DE, Sweany PH, Krasnec JP, Cronn DR. 1979.
Determination of atmospheric halocarbons by a temperature programmed gas
chromatographic freezeout concentration method. J Air Pollut Control
Assoc 27:579.
Ratney RS, Wegman DH, Elkins HB. 1974. In vivo conversion of methylene
chloride to carbon monoxide. Arch Environ Health
28:223-226.
Riley EC, Fasset DW, Sutton WL. 1966. Methylene chloride vapor in
expired air of human subjects. Am Ind Hyg Assoc J 27:341-348.
Rittman BE, McCarty PL. 1980. Utilization of dichloromethane by
suspended and fixed-film bacteria. Appl Environ Microbiol 39:1225-1226
Rodkey FL, Collison HA. 1977. Effect of dihalogenated methanes on the in
vivo production of carbon monoxide and methane by rats. Toxicol Appl
Pharmacol 40:39-47.
Robinson E. 1978. Analysis of Halocarbons in Antarctica. Report 78/13-42
prepared for the National Science Foundation.
Roth RP, Drew RT, Lo RJ, Fouts JR. 1975. Dichloromethane inhalation,
carboxyhemoglobin concentrations, and drug metabolizing enzymes in
rabbits. Toxicol Appl Pharmacol 33:427-437.
Ruth JH. 1986. Odor thresholds and initatlon levels of several chemical
substances. A review. Am Ind Hyg Assoc J 47:A142-A151.
Savolainen H, Pfaffli P, Tengen M, Vainio H. 1977. Biochemical and
behavioral effects of inhalation exposure to tetrachloroethylene and
dichloromethane. J Neuropath Exp Neurol 36:941-949.
-------
References 103
Schvetz BA, Leong BJ, Gehrlng PJ. 1975. The effect of maternally inhaled
trichloroethylene, perchloroethane, methyl chloroform, and methylene
chloride on embryonal and fetal development in mice and rats. Toxicol
Appl Pharmacol 32:84-96.
Serota D, Ulland B. Carlborg F. 1984. Hazleton Chronic Oral Study in
Mice. Food Solvents Workshop No. 1. Methylene Chloride. March 8-9,
Bethesda, MD. In: Anderson ME, Clewell HJ, Gargas ML, Smith FA, Reitz
RH. 1987. Physiologically based pharmacokinetics and the risk assessment
process for methylene chloride. Toxicol Appl Pharmacol 87:185-205.
Singh HB. 1977. Atmospheric halocarbons. Evidence in favor of reduced
average hydroxyl radical concentrations in the troposphere. Geophys Res
Lett 4(3):101-104.
Singh HB et al. 1982. Environ Sci Technol 16:872-880.
Singh HB, Salas LJ, Shigeishi H, Smith AJ, Scribner E, Cavanagh LA.
1979. Atmospheric Distributions, Sources, and Sinks of Selected
Halocarbons, Hydrocarbons, SF6, and N20. Final report submitted to the
Environmental Protection Agency by SRI International, Menlo Park, CA.
EPA-600/3-79-107.
Singh HB, Salas LJ, Smith AJ, Shigeishi. 1981. Measurements of some
potentially hazardous organic chemicals in urban environments. Atmos
Environ 15:601-612.
Singh HB, Salas LJ, Stiles RE. 1983. Selected man-made halogenated
chemicals in the air and oceanic environment. J Geophys Res
88:3675-3683.
Singh HB, Salas LJ, Stiles RE, Shigeishi H. 1980. Atmospheric
Measurements of Selected Hazardous Organic Chemicals. Second Year
Interim Report. Prepared for the Environmental Protection Agency by SRI
International, Menlo Park, CA.
Stewart RD, Fischer TN, Hosko HJ, Peterson JE, Bare tea ED, Dodd HC.
1972. Experimental human exposure to methylene chloride. Arch Environ
Health 25:342-348.
Stewart RD, Hake CL. 1976. Paint remover hazard. J Med Assoc
235(4):398-401.
Stover EL, Kincannon DF. 1983. J Water Pollut Control Fed
55:97-109.
Svirbely JL, Highman B, Alford WF, Von Oettinger WF. 1947. The toxicity
and narcotic action of mono-chloro-mono-bromo-methane with special
reference to inorganic and volatile bromide in blood, urine, and brain.
J Ind Hyg Toxicol 23:383.
Tabak HH et al. 1981. J Water Pollut Control Assoc 53:1503-1518.
-------
104 Section 10
Thilagar AK, Back AM, Kirby PE, et al. 1984a. Evaluation of
dlchloromethane in short-tern in vitro genetic toxicity assays. Environ
Mutagenesis 6:418-419.
Thilagar AK, Kumaroo PV, Clark JJ, Kott A, Back AM, Kirby PE. 1984b.
Induction of chromosome damage by dichloromethane in cultured human
peripheral lymphocytes, CHO cells, and mouse lymphoma LS178Y cells.
Environ Mutagenesis 6:422.
Thilagar AK, Kumaroo V. 1983. Induction of chromosome damage by
methylene chloride in CHO cells. Mutat Res 116:361-367.
Thomas AA, Pinkerton MK, Warden JA. 1972. Effects of low-level
dichloromethane exposure on the spontaneous activity of mice.
In: Proceedings of the 3rd Annual Conference on Environmental
Toxicology. Wright-Patterson Air Force Base, OH: Aerospace Medical
Research Laboratory. AMRL-TR72-130, pp. 185-189.
Ugazio G, Burdino E, Danni 0, Milillo PA. 1973. Hepatoxicity and
lethality of halogenoalkanes. Biochem Soc Trans 1:968-972.
Verschueren K. 1977. Handbook of Environmental Data on Organic
Chemicals. New York: Van Nostrand Reinhold.
Von Oettingen WF, Powell CC, Sharpless NE. Alford WC, Pecora LJ. 1949.
Relation Between the Toxic Action of Chlorinated Methanes and Their
Chemical and Physicochemical Properties. NIH Bulletin 191. Federal
Security Agency, U.S. Public Health Service, National Institutes of
Health.
Weast RC, ed. 1985. CRC Handbook of Chemistry and Physics. 66th ed. Boca
Raton, FL: CRC Press.
Weinstein RS, Diamond SS. 1972. Hepatotoxicity of dichloromethane
(methylene chloride) with continuous inhalation exposure at a low dose
level. In:. Proceedings of the 3rd Annual Conference on Environmental
Toxicology. Wright-Patterson Air Force Base, OH: Aerospace Medical
Research Laboratory. AMRL-TR-72-130, pp. 209-220.
Weinstein RS, Boyd DD, Back KC. 1972. Effects of continuous inhalation
of dichloromethane in the mouse--morphologic and functional
observations. Toxicol Appl Pharmacol 23:660 (cited in EPA 1985c).
Weiss G. 1967. Toxic encephalosis as an occupational hazard with
methylene chloride. Zentralbl Arbeitsmed 17:282-285.
Welch L. 1987. Reports of clinical disease secondary to methylene
chloride exposure--a collection of 141 cases. Unpublished study.
Submitted to OPTS/EPA 3/31.
-------
References 105
* Wlnneke G. 1974. Behavioral effects of methylene chloride and carbon
monoxide as assessed by sensory and psychomotor performance. In:
Xintaraa C, Johnson BL, de Groot I, eds. Behavioral Toxicology.
Washington, DC: U.S. Government Printing Office, pp. 130-144.
Wood PR, Parsons FZ, OeMarco J, et al. 1981. Introductory study of the
biodegradation of ethane and ethene compounds. Presented'at the American
Water Works Association meeting, June.
Yesair DW, Jacques D. Schepis P, Liss RH. 1977. Dose-related
pharmacokinetics of 14C methylene chloride in mice. Fed Proc 36:998
(cited in EPA 1985c).
-------
107
11. GLOSSARY
Acute Exposure--Exposure to a chemical for a duration of 14 days or
less, as specified in the Toxicological Profiles.
Bloconcentratlon Factor (BCF)--The quotient of the concentration of a
chemical in aquatic organisms at a specific time or during a discrete
time period of exposure divided by the concentration in the surrounding
water at the same time or during the same time period.
Carcinogen--A chemical capable of inducing cancer.
Ceiling value (CL)--A concentration of a substance that should not be
exceeded, even instantaneously.
Chronic Exposure--Exposure to a chemical for 365 days or more, as
specified in the Toxicological Profiles.
Developmental Toxicity--The occurrence of adverse effects on the
developing organism that may result from exposure to a chemical prior co
conception (either parent), during prenatal development, or postnatally
to the time of sexual maturation. Adverse developmental effects may be
detected at any point in the life span of the organism.
Embxyotoxlclty and Fetotoxicity--Any toxic effect on the conceptus as a
result of prenatal exposure to a chemical; the distinguishing feature
between the two terms is the stage of development during which the
insult occurred. The terms, as used here, include malformations and
variations, altered growth, and in utero death.
Frank Effect Level (PEL)--That level of exposure which produces a
statistically or biologically significant increase in frequency or
severity of unmistakable adverse effects, such as irreversible
functional impairment or mortality, in an exposed population when
compared with its appropriate control.
EPA Health Advisory--An estimate of acceptable drinking water levels for
a chemical substance based on health effects information. A health
advisory is not a legally enforceable federal standard, but serves as
technical guidance to assist federal, state, and local officials.
Immediately Dangerous to Life or Health (IDLH)--The maximum
environmental concentration of a contaminant from which one could escape
within 30 min without any escape-impairing symptoms or irreversible
health effects.
-------
108 Sec don 11
Intermediate Exposure--Exposure to a chemical for a duration of 15-364
days, as specified in the Toxicological Profiles.
Inmmnologic Toxicity--The occurrence of adverse effects on the immune
system that may result from exposure to environmental agents such as
chemicals.
In vitro--Isolated from the living organism and artificially maintained.
as in a test tube.
In vivo--Occurring within the living organism.
Key Study--An animal or human toxicological study that best illustrates
the nature of the adverse effects produced and the doses associated with
those effects.
Lethal Coneentration(LO) (LCLO)--The lowest concentration of a chemical
in air which has been reported to have caused death in humans or
animals.
Lethal Concentration(SO) (LCso)--A calculated concentration of a
chemical in air to which exposure for a specific length of time is
expected to cause death in 50% of a defined experimental animal
population.
Lethal Dose(LO) (LDLO)--The lowest dose of a chemical introduced by a
route other than inhalation that is expected to have caused death in
humans or animals.
Lethal Dose(50) (U>50)--The dose of a chemical which has been calculated
to cause death in 50% of a defined experimental animal population.
Lowest-Observed-Adverse-Effect Level (LOAEL)--The lowest dose of
chemical in a study or group of studies which produces statistically or
biologically significant increases in frequency or severity of adverse
effects between the exposed population and its appropriate control.
Lowest-Observed-Effect Level (LOEL)--The lowest dose of chemical in a
study or group of studies which produces statistically or biologically
significant increases in frequency or severity of effects between the
exposed population and its appropriate control.
Malformation*--Permanent structural changes that may adversely affect
survival, development, or function.
Minimal Risk Laval--An estimate of daily human exposure to a chemical
that is likely to be without an appreciable risk of deleterious effects
(noncancerous) over a specified duration of exposure.
Mutagen--A substance that causes mutations. A mutation is a change in
the genetic material in a body cell. Mutations can lead to birth
defects, miscarriages, or cancer.
-------
Glossary 109
Neurotoxicity--The occurrence of adverse effects on the nervous system
following exposure to a chemical.
No-Observed-Adverse-Effect Level (NOAEL)--That dose of chemical at which
there are no statistically or biologically significant increases in
frequency or severity of adverse effects seen between the exposed
population and its appropriate control. Effects may be produced at this
dose, but they are not considered to be adverse.
No-Observed-Effect Level (NOEL)--That dose of chemical at which there
are no statistically or biologically significant increases in frequency
or severity of effects seen between the exposed population and its
appropriate control.
Permissible Exposure Limit (PEL)--An allowable exposure level in
workplace air averaged over an 8-h shift.
q.*--The upper-bound estimate of the low-dose slope of the dose-response
curve as determined by the multistage procedure. The q * can be used to
calculate an estimate of carcinogenic potency, the incremental excess
cancer risk per unit of exposure (usually pg/L for water, mg/kg/day for
food, and pg/w? for air).
Reference Dose (RfD)--An estimate (with uncertainty spanning perhaps an
order of magnitude) of the daily exposure of the human population to a
potential hazard that is likely to be without risk of deleterious
effects during a lifetime. The RfD is operationally derived from the
NOAEL (from animal and human studies) by a consistent application of
uncertainty factors that reflect various types of data used to estimate
RfDs and an additional modifying factor, which is based on a
professional judgment of the entire database on the chemical. The RfDs
are not applicable to nonthreshold effects such as cancer.
Reportable Quantity (RQ)--The quantity of a hazardous substance that is
considered reportable under CERCLA. Reportable quantities are: (1) 1 Ib
or greater or (2) for selected substances, an amount established by
regulation either under CERCLA or under Sect. 311 of the Clean Water
Act. Quantities are measured over a 24-h period.
Reproductive ToxicIty--The occurrence of adverse effects on the
reproductive system that may result from exposure to a chemical. The
toxicity may be directed to the reproductive organs and/or the related
endocrine system. The manifestation of such toxicity may be noted as
aIterations-in sexual behavior, fertility, pregnancy outcomes, or
modifications in other functions that are dependent on the integrity of
this system.
Short-Term Exposure Limit (STEL)--The maximum concentration to which
workers can be exposed for up to IS min continually. No more than four
excursions are allowed per day, and there must be at least 60 min
between exposure periods. The dally TLV-TWA may not be exceeded.
-------
110 Section 11
Target Organ ToxicIty--This term covers a broad range of adverse effects
on target organs or physiological systems (e.g., renal, cardiovascular)
extending from those arising through a single limited exposure to those
assumed over a lifetime of exposure to a chemical.
Teratogen--A chemical that causes structural defects that affect the
development of an organism.
Threshold Limit Value (TLV)--A concentration of a substance to which
most workers can be exposed without adverse effect. The TLV may be
expressed as a TWA, as a STEL, or as a CL.
Time-velghted Average (TWA)--An allowable exposure concentration
averaged over a normal 8-h workday or 40-h workweek.
Uncertainty Factor (OF)--A factor used in operationally deriving the RfD
from experimental data. UFs are intended to account for (1) the
variation in sensitivity among the members of the human population,
(2) the uncertainty in extrapolating animal data to the case of humans,
(3) the uncertainty in extrapolating from data obtained in a study that
is of less than lifetime exposure, and (4) the uncertainty in using
LOAEL data rather than NOAEL data. Usually each of these factors is sec
equal to 10.
-------
Ill
APPENDIX: PEER REVIEW
A peer review panel was assembled for methylene chloride. The
panel consisted of Che following members: Dr. Herbert Cornish
(retired). University of Michigan; Dr. Rudolph Jaeger (consultant), New
York University Medical Center; and Mr. L. Skory (retired), Dow Chemical
Company. These experts collectively have knowledge of methylene
chloride's physical and chemical properties, toxicokinetics, key health
end points, mechanisms of action, human and animal exposure, and
quantification of risk to humans. All reviewers were selected in
conformity with the conditions for peer review specified in the
Superfund Amendments and Reauthorization Act of 1986, Section 110.
A Joint panel of scientists from ATSDR and EPA has reviewed the
peer reviewers' comments and determined which comments will be included
in the profile. A listing of the peer reviewers' comments not
incorporated in the profile, with a brief explanation of the rationale
for their exclusion, exists as part of the administrative record for
this compound. A list of databases reviewed and a list of unpublished
documents cited are also included in the administrative record.
The citation of the peer review panel should not be understood to
imply their approval of the profile's final content. The responsibility
for the content of this profile lies with the Agency for Toxic
Substances and Disease Registry.
------- |